diff --git a/docs/formats/core-data-regions.md b/docs/formats/core-data-regions.md
index 3f5255e..32ed38f 100644
--- a/docs/formats/core-data-regions.md
+++ b/docs/formats/core-data-regions.md
@@ -2500,6 +2500,53 @@ Neither of these decodes any record's *fields*. What is now settled is the
 shape the decoder has to handle: uniform stride per type, 4-byte aligned, with
 one named exception carrying three strides.
 
+## Tie: the "vertex positions" claim does not survive a stride test (2026-10-11)
+
+**Range measured:** level 0, one class, one 58-quadword packet region.
+
+The claim from earlier reads, `i16[0..2]` of a 16-byte element are the vertex
+positions, and 95,612 vertices were "measured" on that reading. A raw dump of
+one packet kills it:
+
+    0000df20  00900000  075006c0  094000c0
+    1f736c63  00544848  00281506  0d40001b
+    0d400a90  ffff00ff  00010ef0  80004253
+    4846a9e3  48a44001  47f40000  46d0b0de
+    0000ee50  00c00000  08a007e0  099000f0   <- group repeats at +64
+    0f807e72  01484848  00321208  0cf00017
+    0cf00ab0  ffff00ff  00020e60  80002e46
+    4858389a  48a44001  47f40000  46d7bbe3
+
+**The first 16 bytes are not a vertex at all** -- they are the packet's own
+header material: `0x0000df20` is not a coordinate and the following words are
+the vif/material words. The 16-byte group at +0 recurs at +64 and +128 with
+identical structure (a small i16, then 0, 0, then an index) and its three
+instances carry the values -8416, -4528, -784. So the stride is **not** 16
+throughout: some elements are 4 bytes, some 16, and the run length varies.
+
+**The period-4 marker does not generalise either.** Grouping every fourth
+16-byte element by the high byte of `i16[3]` gives marker 0 (n 9,204), 0x48
+(n 4,140), 0xff (n 4,912) and 0x01 (n 1,137), and only 0x48 shows a
+plausible position signature -- `i16[1]` extent 425 against `i16[0]` and
+`i16[2]` at 65,535, which is the height axis of a flat object. But the same
+marker 0 bucket has all three slots spanning the full `i16` range, so the
+bucket does not select a layout.
+
+**Two candidate vertex bases were measured and neither clusters.** With
+`packet + vert_ofs` the per-class extents run median 64,976 and p90 65,517;
+with `class + vert_ofs` they run median 55,213 and p90 64,352. Both span the
+whole `i16` range, whereas a real position triple in a level-class local frame
+must span a fraction of it. `vert_ofs + vert_size + scissor_size` is the
+region length, so the region bounds are right -- what is wrong is the element
+layout inside it.
+
+**Consequence for earlier claims, stated plainly.** The 95,612-vertex
+measurement and the 82.5% texcoord fixedness figure were both computed on the
+16-byte reading and are not superseded by this -- they are untested against the
+correct stride, which is not yet known. The LOD1/LOD2-sharing test
+(96.1% same class against 0.4% different) remains the strongest evidence that
+the first slots are positional, and it is insensitive to stride.
+
 ## Most of the chunk container is level-independent
 
 Comparing every chunk record against the same record index in the other 26