diff --git a/Source/Diagnostics/BTDiagnostics.H b/Source/Diagnostics/BTDiagnostics.H
index ab894da69c2..f6c44c777ea 100644
--- a/Source/Diagnostics/BTDiagnostics.H
+++ b/Source/Diagnostics/BTDiagnostics.H
@@ -399,8 +399,6 @@ private:
         lab-frame data. */
     void InitializeParticleFunctors () override;
 
-    /** Update total number of particles flushed for all species for ith snapshot */
-    void UpdateTotalParticlesFlushed(int i_buffer);
     /** Reset total number of particles in the particle buffer to 0 for ith snapshot */
     void ResetTotalParticlesInBuffer(int i_buffer);
     /** Clear particle data stored in the particle buffer */
diff --git a/Source/Diagnostics/BTDiagnostics.cpp b/Source/Diagnostics/BTDiagnostics.cpp
index 0e517e8190c..f7965cd2688 100644
--- a/Source/Diagnostics/BTDiagnostics.cpp
+++ b/Source/Diagnostics/BTDiagnostics.cpp
@@ -129,7 +129,6 @@ void BTDiagnostics::DerivedInitData ()
         }
     }
     m_particles_buffer.resize(m_num_buffers);
-    m_totalParticles_flushed_already.resize(m_num_buffers);
     m_totalParticles_in_buffer.resize(m_num_buffers);
 
     // check that simulation can fill all BTD snapshots
@@ -1065,12 +1064,12 @@ BTDiagnostics::Flush (int i_buffer, bool force_flush)
         }
     }
     m_flush_format->WriteToFile(
-        m_varnames, m_mf_output[i_buffer], m_geom_output[i_buffer], warpx.getistep(),
-        labtime, m_output_species[i_buffer], nlev_output, file_name, m_file_min_digits,
+        m_varnames, m_mf_output.at(i_buffer), m_geom_output.at(i_buffer), warpx.getistep(),
+        labtime,
+        m_output_species.at(i_buffer), nlev_output, file_name, m_file_min_digits,
         m_plot_raw_fields, m_plot_raw_fields_guards,
-        use_pinned_pc, isBTD, i_buffer, m_buffer_flush_counter[i_buffer],
-        m_max_buffer_multifabs[i_buffer], m_geom_snapshot[i_buffer][0], isLastBTDFlush,
-        m_totalParticles_flushed_already[i_buffer]);
+        use_pinned_pc, isBTD, i_buffer, m_buffer_flush_counter.at(i_buffer),
+        m_max_buffer_multifabs.at(i_buffer), m_geom_snapshot.at(i_buffer).at(0), isLastBTDFlush);
 
     // Rescaling the box for plotfile after WriteToFile. This is because, for plotfiles, when writing particles, amrex checks if the particles are within the bounds defined by the box. However, in BTD, particles can be (at max) 1 cell outside the bounds of the geometry. So we keep a one-cell bigger box for plotfile when writing out the particle data and rescale after.
     if (m_format == "plotfile") {
@@ -1104,7 +1103,6 @@ BTDiagnostics::Flush (int i_buffer, bool force_flush)
     NullifyFirstFlush(i_buffer);
     // if particles are selected for output then update and reset counters
     if (!m_output_species_names.empty()) {
-        UpdateTotalParticlesFlushed(i_buffer);
         ResetTotalParticlesInBuffer(i_buffer);
         ClearParticleBuffer(i_buffer);
     }
@@ -1271,10 +1269,10 @@ void BTDiagnostics::MergeBuffersForPlotfile (int i_snapshot)
                 InterleaveSpeciesHeader(recent_species_Header,snapshot_species_Header,
                                         m_output_species_names[i], m_buffer_flush_counter[i_snapshot]);
                 if (BufferSpeciesHeader.m_total_particles == 0) { continue; }
-                if (m_totalParticles_flushed_already[i_snapshot][i]==0) {
-                WARPX_ALWAYS_ASSERT_WITH_MESSAGE(
-                    std::rename(recent_ParticleHdrFilename.c_str(), snapshot_ParticleHdrFilename.c_str()) == 0,
-                    std::string("Renaming ").append(recent_ParticleHdrFilename).append(" to ").append(snapshot_ParticleHdrFilename).append(" has failed"));
+                if (!amrex::FileExists(snapshot_ParticleHdrFilename)) {
+                    WARPX_ALWAYS_ASSERT_WITH_MESSAGE(
+                        std::rename(recent_ParticleHdrFilename.c_str(), snapshot_ParticleHdrFilename.c_str()) == 0,
+                        std::string("Renaming ").append(recent_ParticleHdrFilename).append(" to ").append(snapshot_ParticleHdrFilename).append(" has failed"));
                 } else {
                     InterleaveParticleDataHeader(recent_ParticleHdrFilename,
                                                  snapshot_ParticleHdrFilename);
@@ -1435,10 +1433,8 @@ BTDiagnostics::InitializeParticleBuffer ()
     const MultiParticleContainer& mpc = warpx.GetPartContainer();
     for (int i = 0; i < m_num_buffers; ++i) {
         m_particles_buffer[i].resize(m_output_species_names.size());
-        m_totalParticles_flushed_already[i].resize(m_output_species_names.size());
         m_totalParticles_in_buffer[i].resize(m_output_species_names.size());
         for (int isp = 0; isp < m_particles_buffer[i].size(); ++isp) {
-            m_totalParticles_flushed_already[i][isp] = 0;
             m_totalParticles_in_buffer[i][isp] = 0;
             m_particles_buffer[i][isp] = std::make_unique<PinnedMemoryParticleContainer>(WarpX::GetInstance().GetParGDB());
             const int idx = mpc.getSpeciesID(m_output_species_names[isp]);
@@ -1489,15 +1485,6 @@ BTDiagnostics::PrepareParticleDataForOutput()
     }
 }
 
-void
-BTDiagnostics::UpdateTotalParticlesFlushed(int i_buffer)
-{
-    for (int isp = 0; isp < m_totalParticles_flushed_already[i_buffer].size(); ++isp) {
-        m_totalParticles_flushed_already[i_buffer][isp] += static_cast<int>(
-            m_particles_buffer[i_buffer][isp]->TotalNumberOfParticles());
-    }
-}
-
 void
 BTDiagnostics::ResetTotalParticlesInBuffer(int i_buffer)
 {
diff --git a/Source/Diagnostics/BoundaryScrapingDiagnostics.cpp b/Source/Diagnostics/BoundaryScrapingDiagnostics.cpp
index c85dbd6b226..11ffce02f09 100644
--- a/Source/Diagnostics/BoundaryScrapingDiagnostics.cpp
+++ b/Source/Diagnostics/BoundaryScrapingDiagnostics.cpp
@@ -102,15 +102,6 @@ BoundaryScrapingDiagnostics::InitializeParticleBuffer ()
             m_output_species[i_buffer].push_back(ParticleDiag(m_diag_name, species_name, pc, bnd_buffer));
         }
     }
-    // Initialize total number of particles flushed
-    m_totalParticles_flushed_already.resize(m_num_buffers);
-    for (int i_buffer = 0; i_buffer < m_num_buffers; ++i_buffer) {
-        int const n_species = static_cast<int>(m_output_species_names.size());
-        m_totalParticles_flushed_already[i_buffer].resize(n_species);
-        for (int i_species=0; i_species<n_species; i_species++) {
-            m_totalParticles_flushed_already[i_buffer][i_species] = 0;
-        }
-    }
 }
 
 bool
@@ -157,11 +148,13 @@ BoundaryScrapingDiagnostics::Flush (int i_buffer, bool /* force_flush */)
     const std::string file_prefix = m_file_prefix + "/particles_at_" + particle_buffer.boundaryName(i_buffer);
 
     m_flush_format->WriteToFile(
-        m_varnames, m_mf_output[i_buffer], m_geom_output[i_buffer], warpx.getistep(),
-        warpx.gett_new(0), m_output_species[i_buffer], nlev_output, file_prefix,
+        m_varnames, m_mf_output.at(i_buffer), m_geom_output.at(i_buffer), warpx.getistep(),
+        warpx.gett_new(0),
+        m_output_species.at(i_buffer),
+        nlev_output, file_prefix,
         m_file_min_digits, false, false, use_pinned_pc, isBTD,
         warpx.getistep(0), bufferID, numBTDBuffers, geom,
-        isLastBTD, m_totalParticles_flushed_already[i_buffer]);
+        isLastBTD);
 
     // Now that the data has been written out, clear out the buffer
     particle_buffer.clearParticles(i_buffer);
diff --git a/Source/Diagnostics/Diagnostics.H b/Source/Diagnostics/Diagnostics.H
index 53ce319d747..c0d2a9f0d53 100644
--- a/Source/Diagnostics/Diagnostics.H
+++ b/Source/Diagnostics/Diagnostics.H
@@ -309,11 +309,6 @@ protected:
     /** Vector of pointers to functors to compute particle output per species*/
     amrex::Vector< std::unique_ptr<ComputeParticleDiagFunctor> > m_all_particle_functors;
 
-    /** Vector of total number of particles previously flushed, per species, per snapshot.
-     *  The first vector is for total number of snapshots and second vector loops
-     *  over the total number of species selected for diagnostics.
-     */
-    amrex::Vector< amrex::Vector <int> > m_totalParticles_flushed_already;
     /** Vector of total number of particles in the buffer, per species, per snapshot.
      *  The first vector is for total number of snapshots and second vector loops
      *  over the total number of species selected for diagnostics.
diff --git a/Source/Diagnostics/FlushFormats/FlushFormat.H b/Source/Diagnostics/FlushFormats/FlushFormat.H
index 403e9df7857..65741e4ff20 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormat.H
+++ b/Source/Diagnostics/FlushFormats/FlushFormat.H
@@ -24,8 +24,7 @@ public:
         bool isBTD = false, int snapshotID = -1,
         int bufferID = 1, int numBuffers = 1,
         const amrex::Geometry& full_BTD_snapshot = amrex::Geometry(),
-        bool isLastBTDFlush = false,
-        const amrex::Vector<int>& totalParticlesFlushedAlready = amrex::Vector<int>() ) const = 0;
+        bool isLastBTDFlush = false) const = 0;
 
     FlushFormat () = default;
     virtual ~FlushFormat() = default;
diff --git a/Source/Diagnostics/FlushFormats/FlushFormatAscent.H b/Source/Diagnostics/FlushFormats/FlushFormatAscent.H
index 228e4bc5cf6..9d8d3fcd7d2 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormatAscent.H
+++ b/Source/Diagnostics/FlushFormats/FlushFormatAscent.H
@@ -41,8 +41,7 @@ public:
         bool isBTD = false, int snapshotID = -1,
         int bufferID = 1, int numBuffers = 1,
         const amrex::Geometry& full_BTD_snapshot = amrex::Geometry(),
-        bool isLastBTDFlush = false,
-        const amrex::Vector<int>& totalParticlesFlushedAlready = amrex::Vector<int>() ) const override;
+        bool isLastBTDFlush = false ) const override;
 
 #ifdef AMREX_USE_ASCENT
     /** \brief Do in-situ visualization for particle data.
diff --git a/Source/Diagnostics/FlushFormats/FlushFormatAscent.cpp b/Source/Diagnostics/FlushFormats/FlushFormatAscent.cpp
index 980047e3b46..abfba37cd15 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormatAscent.cpp
+++ b/Source/Diagnostics/FlushFormats/FlushFormatAscent.cpp
@@ -21,7 +21,7 @@ FlushFormatAscent::WriteToFile (
     const bool /*use_pinned_pc*/,
     bool isBTD, int /*snapshotID*/, int /*bufferID*/, int /*numBuffers*/,
     const amrex::Geometry& /*full_BTD_snapshot*/,
-    bool /*isLastBTDFlush*/, const amrex::Vector<int>& /* totalParticlesFlushedAlready*/) const
+    bool /*isLastBTDFlush*/) const
 {
 #ifdef AMREX_USE_ASCENT
     WARPX_PROFILE("FlushFormatAscent::WriteToFile()");
diff --git a/Source/Diagnostics/FlushFormats/FlushFormatCheckpoint.H b/Source/Diagnostics/FlushFormats/FlushFormatCheckpoint.H
index f6aad226d75..5c26ac97f61 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormatCheckpoint.H
+++ b/Source/Diagnostics/FlushFormats/FlushFormatCheckpoint.H
@@ -28,8 +28,7 @@ class FlushFormatCheckpoint final : public FlushFormatPlotfile
         bool isBTD = false, int snapshotID = -1,
         int bufferID = 1, int numBuffers = 1,
         const amrex::Geometry& full_BTD_snapshot = amrex::Geometry(),
-        bool isLastBTDFlush = false,
-        const amrex::Vector<int>& totalParticlesFlushedAlready = amrex::Vector<int>() ) const final;
+        bool isLastBTDFlush = false) const final;
 
     void CheckpointParticles (const std::string& dir,
                               const amrex::Vector<ParticleDiag>& particle_diags) const;
diff --git a/Source/Diagnostics/FlushFormats/FlushFormatCheckpoint.cpp b/Source/Diagnostics/FlushFormats/FlushFormatCheckpoint.cpp
index 5f59cd723da..d77437fb931 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormatCheckpoint.cpp
+++ b/Source/Diagnostics/FlushFormats/FlushFormatCheckpoint.cpp
@@ -39,7 +39,7 @@ FlushFormatCheckpoint::WriteToFile (
         bool /*isBTD*/, int /*snapshotID*/,
         int /*bufferID*/, int /*numBuffers*/,
         const amrex::Geometry& /*full_BTD_snapshot*/,
-        bool /*isLastBTDFlush*/, const amrex::Vector<int>& /* totalParticlesFlushedAlready*/) const
+        bool /*isLastBTDFlush*/) const
 {
     WARPX_PROFILE("FlushFormatCheckpoint::WriteToFile()");
 
diff --git a/Source/Diagnostics/FlushFormats/FlushFormatOpenPMD.H b/Source/Diagnostics/FlushFormats/FlushFormatOpenPMD.H
index 88380407f5e..141760ac2a3 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormatOpenPMD.H
+++ b/Source/Diagnostics/FlushFormats/FlushFormatOpenPMD.H
@@ -40,8 +40,7 @@ public:
         bool isBTD = false, int snapshotID = -1,
         int bufferID = 1, int numBuffers = 1,
         const amrex::Geometry& full_BTD_snapshot = amrex::Geometry(),
-        bool isLastBTDFlush = false,
-        const amrex::Vector<int>& totalParticlesFlushedAlready = amrex::Vector<int>() ) const override;
+        bool isLastBTDFlush = false ) const override;
 
     ~FlushFormatOpenPMD () override = default;
 
diff --git a/Source/Diagnostics/FlushFormats/FlushFormatOpenPMD.cpp b/Source/Diagnostics/FlushFormats/FlushFormatOpenPMD.cpp
index 3b7006243e7..e0c8c4ef2d6 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormatOpenPMD.cpp
+++ b/Source/Diagnostics/FlushFormats/FlushFormatOpenPMD.cpp
@@ -126,7 +126,7 @@ FlushFormatOpenPMD::WriteToFile (
     const bool use_pinned_pc,
     bool isBTD, int snapshotID, int bufferID, int numBuffers,
     const amrex::Geometry& full_BTD_snapshot,
-    bool isLastBTDFlush, const amrex::Vector<int>& totalParticlesFlushedAlready) const
+    bool isLastBTDFlush) const
 {
     WARPX_PROFILE("FlushFormatOpenPMD::WriteToFile()");
     const std::string& filename = amrex::Concatenate(prefix, iteration[0], file_min_digits);
@@ -164,7 +164,7 @@ FlushFormatOpenPMD::WriteToFile (
 
     // particles: all (reside only on locally finest level)
     m_OpenPMDPlotWriter->WriteOpenPMDParticles(
-        particle_diags, static_cast<amrex::Real>(time), use_pinned_pc, isBTD, isLastBTDFlush, totalParticlesFlushedAlready);
+        particle_diags, static_cast<amrex::Real>(time), use_pinned_pc, isBTD, isLastBTDFlush);
 
     // signal that no further updates will be written to this iteration
     m_OpenPMDPlotWriter->CloseStep(isBTD, isLastBTDFlush);
diff --git a/Source/Diagnostics/FlushFormats/FlushFormatPlotfile.H b/Source/Diagnostics/FlushFormats/FlushFormatPlotfile.H
index 486dcc3b5ee..c62056b8907 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormatPlotfile.H
+++ b/Source/Diagnostics/FlushFormats/FlushFormatPlotfile.H
@@ -35,8 +35,7 @@ public:
         bool isBTD = false, int snapshotID = -1,
         int bufferID = 1, int numBuffers = 1,
         const amrex::Geometry& full_BTD_snapshot = amrex::Geometry(),
-        bool isLastBTDFlush = false,
-        const amrex::Vector<int>& totalParticlesFlushedAlready = amrex::Vector<int>() ) const override;
+        bool isLastBTDFlush = false) const override;
 
     /** Write general info of the run into the plotfile */
     void WriteJobInfo(const std::string& dir) const;
diff --git a/Source/Diagnostics/FlushFormats/FlushFormatPlotfile.cpp b/Source/Diagnostics/FlushFormats/FlushFormatPlotfile.cpp
index df73ed34c94..970d9a504d2 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormatPlotfile.cpp
+++ b/Source/Diagnostics/FlushFormats/FlushFormatPlotfile.cpp
@@ -65,7 +65,7 @@ FlushFormatPlotfile::WriteToFile (
     const bool /*use_pinned_pc*/,
     bool isBTD, int snapshotID,  int bufferID, int numBuffers,
     const amrex::Geometry& /*full_BTD_snapshot*/,
-    bool isLastBTDFlush, const amrex::Vector<int>& /* totalParticlesFlushedAlready*/) const
+    bool isLastBTDFlush) const
 {
     WARPX_PROFILE("FlushFormatPlotfile::WriteToFile()");
     auto & warpx = WarpX::GetInstance();
@@ -340,9 +340,9 @@ FlushFormatPlotfile::WriteWarpXHeader(
 void
 FlushFormatPlotfile::WriteParticles(const std::string& dir,
                                     const amrex::Vector<ParticleDiag>& particle_diags,
-                                    const amrex::Real time, bool isBTD) const
+                                    const amrex::Real time,
+                                    bool isBTD) const
 {
-
     for (const auto& part_diag : particle_diags) {
         WarpXParticleContainer* pc = part_diag.getParticleContainer();
         PinnedMemoryParticleContainer* pinned_pc = part_diag.getPinnedParticleContainer();
diff --git a/Source/Diagnostics/FlushFormats/FlushFormatSensei.H b/Source/Diagnostics/FlushFormats/FlushFormatSensei.H
index 54eb7099ba4..d2ec9a5a4e0 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormatSensei.H
+++ b/Source/Diagnostics/FlushFormats/FlushFormatSensei.H
@@ -61,8 +61,7 @@ public:
         bool isBTD = false, int snapshotID = -1,
         int bufferID = 1, int numBuffers = 1,
         const amrex::Geometry& full_BTD_snapshot = amrex::Geometry(),
-        bool isLastBTDFlush = false,
-        const amrex::Vector<int>& totalParticlesFlushedAlready = amrex::Vector<int>() ) const override;
+        bool isLastBTDFlush = false) const override;
 
     /** \brief Do in-situ visualization for particle data.
      * \param[in] particle_diags Each element of this vector handles output of 1 species.
diff --git a/Source/Diagnostics/FlushFormats/FlushFormatSensei.cpp b/Source/Diagnostics/FlushFormats/FlushFormatSensei.cpp
index e162b8b3121..348e1da4a00 100644
--- a/Source/Diagnostics/FlushFormats/FlushFormatSensei.cpp
+++ b/Source/Diagnostics/FlushFormats/FlushFormatSensei.cpp
@@ -53,14 +53,13 @@ FlushFormatSensei::WriteToFile (
     bool plot_raw_fields, bool plot_raw_fields_guards,
     const bool use_pinned_pc,
     bool isBTD, int /*snapshotID*/, int /*bufferID*/, int /*numBuffers*/,
-    const amrex::Geometry& /*full_BTD_snapshot*/, bool /*isLastBTDFlush*/,
-    const amrex::Vector<int>& totalParticlesFlushedAlready) const
+    const amrex::Geometry& /*full_BTD_snapshot*/, bool /*isLastBTDFlush*/) const
 {
     amrex::ignore_unused(
         geom, nlev, prefix, file_min_digits,
         plot_raw_fields, plot_raw_fields_guards,
-        use_pinned_pc,
-        totalParticlesFlushedAlready);
+        use_pinned_pc
+    );
 
 #ifndef AMREX_USE_SENSEI_INSITU
     amrex::ignore_unused(varnames, mf, iteration, time, particle_diags,
diff --git a/Source/Diagnostics/FullDiagnostics.cpp b/Source/Diagnostics/FullDiagnostics.cpp
index 4f1e47a2a52..fd329a38220 100644
--- a/Source/Diagnostics/FullDiagnostics.cpp
+++ b/Source/Diagnostics/FullDiagnostics.cpp
@@ -133,8 +133,9 @@ FullDiagnostics::Flush ( int i_buffer, bool /* force_flush */ )
     auto & warpx = WarpX::GetInstance();
 
     m_flush_format->WriteToFile(
-        m_varnames, m_mf_output[i_buffer], m_geom_output[i_buffer], warpx.getistep(),
-        warpx.gett_new(0), m_output_species[i_buffer], nlev_output, m_file_prefix,
+        m_varnames, m_mf_output.at(i_buffer), m_geom_output.at(i_buffer), warpx.getistep(),
+        warpx.gett_new(0),
+        m_output_species.at(i_buffer), nlev_output, m_file_prefix,
         m_file_min_digits, m_plot_raw_fields, m_plot_raw_fields_guards);
 
     FlushRaw();
diff --git a/Source/Diagnostics/OpenPMDHelpFunction.H b/Source/Diagnostics/OpenPMDHelpFunction.H
index 9db4b9fb194..d2f2c4f9f9d 100644
--- a/Source/Diagnostics/OpenPMDHelpFunction.H
+++ b/Source/Diagnostics/OpenPMDHelpFunction.H
@@ -14,7 +14,25 @@
 #include <string>
 
 
+/** Determine the preferred file ending if unspecified
+ *
+ * @return file ending without the "."
+ */
 std::string
 WarpXOpenPMDFileType ();
 
+#ifdef WARPX_USE_OPENPMD
+/** Determine how many particles were already written in this species and step
+ *
+ * This checks for a particle species the current size of the id attribute, if it exists,
+ * and if it does it takes its extent as the number of particles already on disk.
+ *
+ * Note that this checks declared size, not necessarily written size.
+ *
+ * @return exisitng extent of the "id" attribute or zero.
+ */
+unsigned long
+num_already_flushed (openPMD::ParticleSpecies & currSpecies);
+#endif
+
 #endif  // WARPX_OPENPMDHELPFUNCTION_H_
diff --git a/Source/Diagnostics/OpenPMDHelpFunction.cpp b/Source/Diagnostics/OpenPMDHelpFunction.cpp
index a898c97b6b4..6170249b52b 100644
--- a/Source/Diagnostics/OpenPMDHelpFunction.cpp
+++ b/Source/Diagnostics/OpenPMDHelpFunction.cpp
@@ -27,3 +27,23 @@ WarpXOpenPMDFileType ()
 #endif // WARPX_USE_OPENPMD
     return openPMDFileType;
 }
+
+#ifdef WARPX_USE_OPENPMD
+unsigned long
+num_already_flushed (openPMD::ParticleSpecies & currSpecies)
+{
+    const auto *const scalar = openPMD::RecordComponent::SCALAR;
+
+    unsigned long ParticleFlushOffset = 0;
+
+    if (currSpecies.contains("id")) {
+        if (currSpecies["id"].contains(scalar)) {
+            if (!currSpecies["id"][scalar].empty()) {
+                ParticleFlushOffset = currSpecies["id"][scalar].getExtent().at(0);
+            }
+        }
+    }
+
+    return ParticleFlushOffset;
+}
+#endif
diff --git a/Source/Diagnostics/WarpXOpenPMD.H b/Source/Diagnostics/WarpXOpenPMD.H
index e3b7b893d0a..4597dacd9ae 100644
--- a/Source/Diagnostics/WarpXOpenPMD.H
+++ b/Source/Diagnostics/WarpXOpenPMD.H
@@ -125,8 +125,7 @@ public:
               amrex::Real time,
               bool use_pinned_pc = false,
               bool isBTD = false,
-              bool isLastBTDFlush = false,
-              const amrex::Vector<int>& totalParticlesFlushedAlready = amrex::Vector<int>());
+              bool isLastBTDFlush = false);
 
   /** Write out all openPMD fields for all active MR levels
    *
@@ -290,9 +289,9 @@ private:
    * @param[in] int_comp_names The int attribute names, from WarpX
    * @param[in] charge         Charge of the particles (note: fix for ions)
    * @param[in] mass           Mass of the particles
+   * @param[inout] ParticleFlushOffset previously flushed number of particles in BTD
    * @param[in] isBTD is this a backtransformed diagnostics (BTD) write?
    * @param[in] isLastBTDFlush is this the last time we will flush this BTD station?
-   * @param[in] ParticleFlushOffset previously flushed number of particles in BTD
    */
   void DumpToFile (ParticleContainer* pc,
             const std::string& name,
@@ -304,8 +303,7 @@ private:
             amrex::ParticleReal charge,
             amrex::ParticleReal mass,
             bool isBTD = false,
-            bool isLastBTDFlush = false,
-            int ParticleFlushOffset = 0);
+            bool isLastBTDFlush = false);
 
   /** Get the openPMD-api filename for openPMD::Series
    *
diff --git a/Source/Diagnostics/WarpXOpenPMD.cpp b/Source/Diagnostics/WarpXOpenPMD.cpp
index 71d96a47927..64411ecf6e4 100644
--- a/Source/Diagnostics/WarpXOpenPMD.cpp
+++ b/Source/Diagnostics/WarpXOpenPMD.cpp
@@ -519,9 +519,11 @@ WarpXOpenPMDPlot::Init (openPMD::Access access, bool isBTD)
 
 void
 WarpXOpenPMDPlot::WriteOpenPMDParticles (const amrex::Vector<ParticleDiag>& particle_diags,
-                  const amrex::Real time, const bool use_pinned_pc,
-                  const bool isBTD, const bool isLastBTDFlush,
-                  const amrex::Vector<int>& totalParticlesFlushedAlready)
+                  const amrex::Real time,
+                  const bool use_pinned_pc,
+                  const bool isBTD,
+                  const bool isLastBTDFlush
+)
 {
 WARPX_PROFILE("WarpXOpenPMDPlot::WriteOpenPMDParticles()");
 
@@ -618,31 +620,15 @@ for (unsigned i = 0, n = particle_diags.size(); i < n; ++i) {
 
     // real_names contains a list of all real particle attributes.
     // real_flags is 1 or 0, whether quantity is dumped or not.
-    {
-        if (isBTD) {
-            DumpToFile(&tmp,
-                particle_diags[i].getSpeciesName(),
-                m_CurrentStep,
-                real_flags,
-                int_flags,
-                real_names, int_names,
-                pc->getCharge(), pc->getMass(),
-                isBTD, isLastBTDFlush,
-                totalParticlesFlushedAlready[i]
-            );
-        } else {
-            DumpToFile(&tmp,
-                particle_diags[i].getSpeciesName(),
-                m_CurrentStep,
-                real_flags,
-                int_flags,
-                real_names, int_names,
-                pc->getCharge(), pc->getMass(),
-                isBTD, isLastBTDFlush,
-                0
-            );
-        }
-    }
+    DumpToFile(&tmp,
+        particle_diags.at(i).getSpeciesName(),
+        m_CurrentStep,
+        real_flags,
+        int_flags,
+        real_names, int_names,
+        pc->getCharge(), pc->getMass(),
+        isBTD, isLastBTDFlush
+    );
 }
 }
 
@@ -657,8 +643,9 @@ WarpXOpenPMDPlot::DumpToFile (ParticleContainer* pc,
                     amrex::ParticleReal const charge,
                     amrex::ParticleReal const mass,
                     const bool isBTD,
-                    const bool isLastBTDFlush,
-                    int ParticleFlushOffset) {
+                    const bool isLastBTDFlush
+)
+{
     WARPX_ALWAYS_ASSERT_WITH_MESSAGE(m_Series != nullptr, "openPMD: series must be initialized");
 
     AMREX_ALWAYS_ASSERT(write_real_comp.size() == pc->NumRealComps());
@@ -672,6 +659,9 @@ WarpXOpenPMDPlot::DumpToFile (ParticleContainer* pc,
     openPMD::Iteration currIteration = GetIteration(iteration, isBTD);
     openPMD::ParticleSpecies currSpecies = currIteration.particles[name];
 
+    // only BTD writes multiple times into the same step, zero for other methods
+    unsigned long ParticleFlushOffset = isBTD ? num_already_flushed(currSpecies) : 0;
+
     // prepare data structures the first time BTD has non-zero particles
     //   we set some of them to zero extent, so we need to time that well
     bool const is_first_flush_with_particles = num_dump_particles > 0 && ParticleFlushOffset == 0;