diff --git a/minimateplus/event_file_io.py b/minimateplus/event_file_io.py
index 5618f72..a7980f1 100644
--- a/minimateplus/event_file_io.py
+++ b/minimateplus/event_file_io.py
@@ -48,7 +48,7 @@ SIDECAR_KIND   = "sfm.event"
 # bumped without a `pip install` re-run — leading to confusing stale
 # version stamps in sidecars.  Bump this constant and CHANGELOG.md
 # together at release time.
-TOOL_VERSION = "0.16.1"
+TOOL_VERSION = "0.20.0"
 
 try:
     # Best-effort: prefer the installed metadata when it's NEWER than the
diff --git a/scripts/backfill_sidecars.py b/scripts/backfill_sidecars.py
index b937e8c..8037d1f 100644
--- a/scripts/backfill_sidecars.py
+++ b/scripts/backfill_sidecars.py
@@ -12,8 +12,20 @@ Walks `<store_root>/<serial>/<filename>` and for each BW event file:
       parsing the BW binary directly (peaks computed from samples).
 
   Clean waveform (.h5):
-    - Skip when <filename>.h5 already exists (idempotent).
-    - Else write from .a5.pkl (preferred) or BW binary parse (fallback).
+    - Regenerated whenever the sidecar is regenerated (sha mismatch
+      OR sidecar.source.tool_version < current TOOL_VERSION OR --force).
+      The .h5 and the sidecar both come from the same decoder output,
+      so if the sidecar is stale the .h5 is too.
+    - Written when missing.
+    - --skip-hdf5 turns off all .h5 writes.
+
+Typical use after a decoder upgrade:
+    1. Pull the new seismo-relay code (which bumped TOOL_VERSION).
+    2. Run this script — every sidecar with an older tool_version
+       stamp regenerates, and the associated .h5 cascade-regenerates.
+    3. Operator review state (review.false_trigger, notes, reviewer)
+       and the sidecar's extensions block are preserved across the
+       regen.
 
 Usage:
     python scripts/backfill_sidecars.py [--store-root PATH]
@@ -123,6 +135,12 @@ def main(argv=None) -> int:
             #      the sidecar was written by a build that includes any
             #      decoder fixes shipped since).
             # Either part failing → regenerate.  --force bypasses both.
+            #
+            # Tracks whether we're regenerating the sidecar this iteration
+            # so the .h5 logic below knows to refresh that too — staleness
+            # of the sidecar implies staleness of the derived .h5 (both
+            # come out of the same decoder).
+            sidecar_stale = True
             if sidecar_path.exists() and not args.force:
                 try:
                     existing = event_file_io.read_sidecar(sidecar_path)
@@ -136,6 +154,7 @@ def main(argv=None) -> int:
                     ver_ok = _vt(src_ver) >= _vt(event_file_io.TOOL_VERSION)
                     if sha_ok and ver_ok:
                         skipped += 1
+                        sidecar_stale = False
                         continue
                     if sha_ok and not ver_ok:
                         log.info(
@@ -281,12 +300,23 @@ def main(argv=None) -> int:
                     extensions=preserved_ext,
                 )
 
-                # Also emit the .h5 clean-waveform file when missing OR when
-                # --force was passed (so a re-backfill picks up decoder fixes).
+                # Also emit the .h5 clean-waveform file when:
+                #   - it's missing, OR
+                #   - --force was passed, OR
+                #   - the sidecar is being regenerated this iteration
+                #     (sha mismatch / tool_version too old).  The .h5 and
+                #     the sidecar are both derived from the same decoder
+                #     output, so if the sidecar is stale, so is the .h5.
+                #     This is the path that recovers from the broken-
+                #     int16-LE codec era — bumping TOOL_VERSION to 0.20.0+
+                #     marks every pre-codec sidecar stale, which now
+                #     correctly cascades to .h5 regeneration too.
                 hdf5_path = store.hdf5_path_for(serial, path.name)
                 hdf5_filename = hdf5_path.name if hdf5_path.exists() else None
                 hdf5_action = "kept"
-                need_h5 = not args.skip_hdf5 and (args.force or not hdf5_path.exists())
+                need_h5 = not args.skip_hdf5 and (
+                    args.force or not hdf5_path.exists() or sidecar_stale
+                )
                 if need_h5:
                     if args.dry_run:
                         hdf5_action = "would (re)write"