diff --git a/docs/formats/core-data-regions.md b/docs/formats/core-data-regions.md
index 10085d1..3491bde 100644
--- a/docs/formats/core-data-regions.md
+++ b/docs/formats/core-data-regions.md
@@ -218,3 +218,27 @@ of that level's data, but 24 of 24 agreeing is a format invariant.
 What a 368-byte record *is* remains unestablished. This is the same position
 the shrub body was in before differential analysis identified its records,
 and the same method is the obvious next step.
+
+### Differential analysis at stride 368: no constant substructure
+
+**Range measured:** level 0, `16047040 .. 16737344`. 1,875 whole 368-byte
+records from the region start; variation checked across the first 60.
+
+**Method:** the same differential analysis that identified the shrub body --
+compare records byte by byte and record which positions differ.
+
+**Result:** **all 368 positions vary.** There is no constant field, no padding
+and no header inside a record. Unlike the shrub body, where differential
+analysis immediately separated a varying payload from a constant two-byte
+tail, this format has nothing constant to separate.
+
+That does not contradict the autocorrelation peak. Checking which byte
+positions carry the 368-stride matches over 20,000 positions: 168 exact 4-byte
+repeats, distributed evenly at 0.84% across all four byte offsets. So whole
+4-byte sequences recur at exactly 368 while no individual position is constant
+-- consistent with records containing entries that repeat at a fixed relative
+index, rather than with a fixed-layout record.
+
+**So the 368 stride stands and the records remain unidentified.** The shrub
+method failed here not because it was the wrong tool but because it needs
+something constant to latch onto, and there is nothing.