diff --git a/docs/re/BACKLOG.md b/docs/re/BACKLOG.md
index 119bb3a1..d599a1ed 100644
--- a/docs/re/BACKLOG.md
+++ b/docs/re/BACKLOG.md
@@ -1048,9 +1048,18 @@ premise was wrong.**
   are cleared for take-off!", the same for s02A/s07A/s08A/s13A. Someone expecting
   a stage-13-specific line would call the generic one wrong while the binding is
   right.
-  ❔ Still open: whether the leading XMA1-mono region is *additional* audio or an
-  alternate take of the same line — the totals above add it to the RIFF sub-waves
-  and would double-count if it is a duplicate.
+  ✅ **(same day) The two parts are SEQUENTIAL SEGMENTS, not duplicates** — so the
+  totals do not double-count and the 48 kHz fit stands. Measured by RMS:
+  `450`/`451`/`452` have a **silent or near-silent** leading region (RMS 0–301
+  against ~9 000 for speech) with the line in the RIFF; `453`/`454` have the line
+  in the **leading** region with a short loud tail in the RIFF.
+  🎯 **That closes the original mystery.** The decoder skips everything before the
+  first `RIFF`. For the first three that discards only silence, so they looked
+  fine (2.8 / 1.6 / 2.2 s); for the last two it discards **the line itself**,
+  leaving 0.14 s and 0.43 s. One rule, two outcomes, depending on which segment
+  holds the speech. ▶️ The fix is now well-posed: emit the leading region **only
+  when it carries signal**, which also avoids the 1524-bank blast radius that
+  sank the earlier attempt.
 * ❌ **(2026-08-25) The `.slb` "multi-subwave" guess is REFUTED, and the voice
   decoder is discarding up to 87 % of a bank.** The record table gives a
   **direct** binding `hokyu_DS_s13A -> VOICE_D_452` where the corpus records the
diff --git a/docs/re/voice-bank-leading-region.md b/docs/re/voice-bank-leading-region.md
index 20779825..85c3f4e9 100644
--- a/docs/re/voice-bank-leading-region.md
+++ b/docs/re/voice-bank-leading-region.md
@@ -178,6 +178,40 @@ Three of the five are decisive; the other two have their only cue at 0.0 s, whic
 tells us nothing in either direction. So **something is genuinely missing from
 these banks** — independent of anything above, and now measured rather than felt.
 
+## ✅ The two parts are SEQUENTIAL SEGMENTS — and that closes the original mystery
+
+The last open question was whether the leading mono region duplicates the RIFF
+sub-wave (in which case adding them would double-count). It does not. Decoding
+both parts of each bank to mono PCM and measuring energy:
+
+| bank | leading | | RIFF | |
+|---|---|---|---|---|
+| | secs | RMS | secs | RMS |
+| `VOICE_D_450` | 0.49 | **158** | 2.82 | 9 898 |
+| `VOICE_D_451` | 0.01 | **0** | 1.58 | 9 128 |
+| `VOICE_D_452` | 0.31 | **301** | 2.18 | 9 061 |
+| `VOICE_D_453` | 2.12 | 9 770 | 0.14 | 14 462 |
+| `VOICE_D_454` | 3.07 | 10 428 | 0.43 | 11 639 |
+
+Two shapes, and no bank has the same content twice:
+
+* in `450`/`451`/`452` the leading region is **silence or near-silence** (RMS 0 to
+  301 against ~9 000 for speech) — a lead-in — and the **RIFF holds the line**;
+* in `453`/`454` the **leading region holds the line** and the RIFF is a short
+  loud tail fragment.
+
+So the parts are sequential segments of one clip. The totals used above do not
+double-count, and the 48 kHz fit stands.
+
+### 🎯 Why `453` and `454` looked broken and the others did not
+
+This is exactly the original symptom. The corpus recorded `450` = 2.8 s,
+`451` = 1.6 s, `452` = 2.2 s — plausible — but `453` = **0.14 s** and
+`454` = **0.43 s**. The decoder skips everything before the first `RIFF`. For the
+first three that discards only silence, so they looked fine; for the last two it
+discards **the line itself**, leaving the trailing fragment. One rule, two
+outcomes, depending on which segment happens to hold the speech.
+
 ## ✅ Each shared bank is ONE generic line
 
 The banks are bound to 3–5 movie slots each, and the movies sharing a bank have