diff --git a/docs/re/structures/mcol-collision.md b/docs/re/structures/mcol-collision.md
index ae71b3f..510a367 100644
--- a/docs/re/structures/mcol-collision.md
+++ b/docs/re/structures/mcol-collision.md
@@ -149,4 +149,43 @@ Worth noting the split was crude — "first half by address", giving 2 509 vs
 partition that isolates a perfect population is stronger evidence than a careful
 one that isolates a good-ish population.
 
-❔ Array B's layout is still unread. That is the next thing.
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+### ✅ A → B is one-to-one, and every count is 1
+
+Filtering array A by the cell-index criteria (so only genuine A records) and
+following each one's pointer, over all **11** objects:
+
+| | |
+|---|---|
+| every A record points at a **distinct** B record | **11 / 11** |
+| every A record's count field is **exactly 1** | **11 / 11** |
+
+Per object the A-record count is the number of **occupied cells** — 110, 118,
+117, 488, 488, 575, 514, 468, 492, 546, 572 — and the total of the count fields
+equals it exactly.
+
+That is the *same* design `REGN` uses: this corpus already records for `REGN`
+that "every occupied cell has count exactly 1 — total items equals occupied
+cells". Two sibling formats, same cell-index convention. It is a further
+independent confirmation of the A-record reading, since the filter and the
+cardinality are unrelated criteria.
+
+### ❌ Array B resisted a first pass, and the tests I reached for were bad ones
+
+I could not read B's record layout this iteration, and both attempts failed in
+ways worth recording rather than retrying:
+
+* **The boundary was off by 8 again.** Dumping from `pointer − 8` (as A's layout
+  needed) produced records that begin with what is plainly the *tail* of the
+  previous structure — a zero and `0x47295092`, the same radius value A's first
+  record carries. Same mistake as the `0x74` check two iterations ago.
+* **The `u16`-index test had no power.** The `0x5C` block holds ~1 232 points, so
+  "is this `u16` below the point count" is satisfied by almost any small value —
+  and duly reported 100 % at seven different offsets. That is the *fourth* time
+  in this pair of formats that a bound-check against a large collection has
+  produced a meaningless 100 %.
+
+❔ So B's layout is open. **What would have power**: B records are 1:1 with
+occupied cells and A already carries the cell's bounding sphere, so a candidate
+field in B can be tested by whether it is spatially consistent with *that
+specific cell* — the same design that worked for `REGN`'s faces, and the same
+design that these two bound-checks lack.
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