diff --git a/docs/formats/core-data-regions.md b/docs/formats/core-data-regions.md
index 309f6bd..a56036e 100644
--- a/docs/formats/core-data-regions.md
+++ b/docs/formats/core-data-regions.md
@@ -368,15 +368,22 @@ statistics below. The matched-control autocorrelation puts the peak at stride
 **What it is made of:**
 
 - **1,185 distinct `u32` values** across 5,780 words.
-- **Mean 6.99 of 8 bytes are zero**, so most records are sparse -- one or two
-  live bytes in eight.
+- **Mean 6.99 of 8 bytes are live** -- the previous revision of this file said
+  "zero", which is inverted and wrong. The live-byte histogram is 0:15, 2:1,
+  4:31, 5:238, 6:461, 7:1030, 8:1114, so most records are nearly full rather
+  than sparse.
 - **549 of 2,890 adjacent pairs (19%) are exact duplicates of each other.** The
   most common 8-byte record, appearing 283 times, is `d7d7d780 d7d7d780` -- a
   4-byte value stored twice. Others follow the same shape: `00051980 00051980`,
   `00082580 00082580`.
 
-**Not decoded.** Sparsity plus repeated entries is what a keyframe or index
-table looks like, but nothing here establishes that, and the duplicated-4-byte
-shape may equally be two adjacent records that happen to share a value.
+**Byte 7 is anomalous.** It takes only **14 distinct values** where bytes 0-6
+take 142-204. Its common values are `0x00` (1378), `0xff` (806) and `0x80`
+(592) -- the high bytes of signed 16-bit values, which is consistent with
+byte 7 being an MSB of something rather than ordinary data. Unexplained.
+
+**Not decoded.** A signed-16-bit reading was tried and does not obviously
+help: the values span -32743..32633, close to the full range, with no
+per-position structure (533, 371, 401 and 187 distinct at positions 0-3).
 Recorded as a characterisation, with its range, so the next attempt starts
 from the composition rather than re-deriving it.