diff --git a/docs/formats/core-data-regions.md b/docs/formats/core-data-regions.md
index 49ef600..13a371f 100644
--- a/docs/formats/core-data-regions.md
+++ b/docs/formats/core-data-regions.md
@@ -495,3 +495,36 @@ Also measured, for the record:
 - `gameplay.bin` peaks at 16 bytes (excess 0.267 at strides 16, 32 and 64).
 - `gs_ram.bin` has almost no stride structure (0.043 at 32) but a lag-8
   correlation of +0.503, so it is smooth rather than tabular.
+
+## Tie class spans: 16-byte unit, 48-byte period (dominant, not universal)
+
+**Range measured:** every tie class span on levels 0, 3, 6 and every third
+level after it -- 386 spans of 16 KB or more, bounded by consecutive class
+offsets.
+
+**Method:** peak-stride autocorrelation with a matched control, over the first
+32,768 bytes of each span.
+
+**Result:**
+
+| peak stride | spans |
+|---|---|
+| 48 | 285 |
+| 16 | 58 |
+| 64 | 29 |
+| 96 | 11 |
+| 24 | 2 |
+| 32 | 1 |
+
+**48 bytes dominates but is not universal**, and the weaker peak is 58 spans
+against 285 -- so unlike the sound bank's 40, this is a majority rather than a
+constant.
+
+Every observed peak is a multiple of 16 (16, 24, 32, 48, 64, 96), which
+suggests a **16-byte base unit** with a 48-byte period arising from how those
+units group, rather than 48 being the record itself.
+
+This is weaker evidence than the sound bank's 40-byte result, which was
+sharply isolated and identical on all 27 levels. Here the peak is weaker
+(0.09-0.22 excess against sound bank's 0.45) and it moves between levels and
+spans. Recorded at the confidence it deserves.