diff --git a/docs/formats/core-data-regions.md b/docs/formats/core-data-regions.md
index 13a371f..9c3fc06 100644
--- a/docs/formats/core-data-regions.md
+++ b/docs/formats/core-data-regions.md
@@ -528,3 +528,40 @@ This is weaker evidence than the sound bank's 40-byte result, which was
 sharply isolated and identical on all 27 levels. Here the peak is weaker
 (0.09-0.22 excess against sound bank's 0.45) and it moves between levels and
 spans. Recorded at the confidence it deserves.
+
+## Two independent measurements agree on moby's 16-byte vertex
+
+The moby part table established `vertex_offset + 16 * vertex_count ==
+next_part` on 43,467 of 43,467 parts, which fixes the vertex stride at 16.
+Autocorrelation over the spans reaches the same number without using that
+result at all.
+
+**Range measured:** moby class spans of 16 KB or more on level 0 -- 60 spans,
+each bounded by consecutive class offsets, measured over the first 32,768
+bytes.
+
+**Method:** peak-stride autocorrelation against a matched control, searching
+strides 4 to 64.
+
+**Result:**
+
+| peak stride | spans |
+|---|---|
+| **16** | **43** |
+| 8 | 8 |
+| 48 | 4 |
+| 32 | 3 |
+| 24 | 2 |
+
+16 dominates, and it is the same 16 the part table produces from a completely
+different argument -- a tiling identity over part records rather than a
+periodicity measurement over span contents.
+
+Two unrelated methods agreeing is worth more than either alone, because the
+autocorrelation would be vulnerable to exactly the kinds of artifact this
+project has already been bitten by: a dominant byte value would inflate it,
+and a period that happened to divide the window would look the same as a real
+one. Neither applies here, and the tiling identity cannot be inflated at all.
+
+This is the strongest form of evidence produced in this project: a structural
+invariant confirmed by two methods that do not share a failure mode.