diff --git a/docs/formats/core-data-regions.md b/docs/formats/core-data-regions.md
index 2a2d526..cf5c700 100644
--- a/docs/formats/core-data-regions.md
+++ b/docs/formats/core-data-regions.md
@@ -319,3 +319,39 @@ The contrast with sky is the point: the same statistic on the same kind of
 question gave a real answer in one region and an inflated one in the other,
 and the only thing that told them apart was whether the control matched the
 byte distribution.
+
+## Sky sub-objects: structure is consistent, stride is not
+
+**Range measured:** every level's sky region, from the count field at `+0x0c`
+through the sub-object offsets at `+0x20`. Each sub-object measured over its
+first 16,384 bytes.
+
+**Method:** as above, peak-stride autocorrelation per sub-object with a
+matched control (the same bytes shuffled, seeded per level and index).
+
+**Field note:** the sub-object count is a `u32` at **`+0x0c`**, not `+0x0a`.
+Reading `+0x0a` gives 327,680 on level 0, which is not a count.
+
+**Result, level 0:** five sub-objects at offsets 365760, 388880, 396432,
+406784 and 414032, of lengths 23120, 7552, 10352, 7248 and 1536. Each has
+internal structure well clear of its matched control.
+
+**But the strides do not repeat across levels.** Recomputing per level:
+
+| sub-object | peak strides seen across levels |
+|---|---|
+| 0 | 4 (x6), 8 (x13), 32, 288 |
+| 1 | 16 (x3), 32 (x6), 288 |
+| 2 | 8, 16 (x5), 256, 288 |
+| 3 | 8, 16 (x6), 216 |
+| 4 | 8, 16 (x3), 512 (x4) |
+
+So the earlier per-index stride table, read off level 0 alone, was
+over-fitted to one level. What is consistent is weaker and more honest: every
+sub-object sits above its matched control, and most peak at a small stride of
+4, 8, 16 or 32, which suggests 16- or 32-bit records whose stride varies with
+content rather than being fixed.
+
+**Level 2's header remains genuinely different**: its count field at `+0x0c`
+reads 196,617 and is unusable, while every other level yields a plausible
+count. Whatever makes it different is still unexplained.