diff --git a/docs/formats/core-data-regions.md b/docs/formats/core-data-regions.md
index 3b5f442..0534c55 100644
--- a/docs/formats/core-data-regions.md
+++ b/docs/formats/core-data-regions.md
@@ -1385,3 +1385,45 @@ and it also disagreed with `bucket_rule` on the byte-0 count (1,208 against
 Recorded because the two numbers came from the same run and only the discrepancy
 exposed the probe as wrong. The lesson is narrow and worth stating: when a
 one-off probe and a committed helper disagree, check the probe first.
+
+## Chunk record bodies: what was ruled out
+
+With the framing settled (leading two bytes = record index), the body is bytes
+`2..len`. Four probes on it, mostly negative.
+
+**No count field.** For every chunk type, every `u16` and `u32` position in the
+first 64 body bytes, at element strides 1, 2, 3, 4, 6, 8, 12 and 16: does the
+stored value equal `(record_len - offset) / stride` on 90% or more of records?
+**No type produced a hit.** The record does not carry an element count near its
+head.
+
+**The body is dense, not float-dominated.** For the largest type (2,430 records,
+326-byte bodies):
+
+    f32 reads within +/-5000 of origin : 74%
+    uniform-random control              : 49%
+    zero-byte fraction                  : 13%
+
+Above baseline but far short of what the tie blocks look like (53-64% against
+16%, with 43% zero bytes). The chunk bodies are denser and less float-shaped than
+tie geometry.
+
+**There is an index-like region near the tail.** In the largest type, **12 of 163**
+`u16` slots have a maximum below `0x1000` -- too small for float or half-float
+data, so those slots look like indices or small counts. They cluster at slots
+111-121 and 130-131.
+
+### A sample-size correction
+
+Dumping six records of one chunk showed slots 112-119 **zero on every record** and
+a long run of other constant slots, which read as "the record is mostly a
+per-chunk template". Measured properly across the 1,171 chunks with at least 8
+records:
+
+    u16 slots constant across every record in their chunk : 15,422 of 164,390 (9.4%)
+    chunks whose records are ENTIRELY constant             : 0 of 1,171
+
+So 9.4%, and no chunk is a template. Six records looked like a majority because
+that chunk's tail happens to carry shared constants -- the per-type figures range
+from 9.4% overall to 55.6% on one type. A pooled figure over all types would have
+hidden that spread again, so it is reported per type as well.