Measure tie class spans: 16-byte unit, 48-byte period, dominant not universal

Range measured: every tie class span of 16 KB or more on levels 0, 3, 6 and
every third level after -- 386 spans, bounded by consecutive class offsets.

Method: peak-stride autocorrelation with a matched control over the first
32768 bytes of each span.

  stride 48   285 spans
  stride 16    58
  stride 64    29
  stride 96    11
  stride 24     2
  stride 32     1

48 bytes dominates but is not universal: 58 spans peak at 16 against 285 at
48, so this is a majority rather than a constant. Every observed peak is a
multiple of 16, suggesting a 16-byte base unit with 48 arising from how those
units group rather than 48 being the record.

This is weaker than the sound bank's 40-byte result and is recorded at the
confidence it deserves. That one was sharply isolated -- 0.454 excess at 40
against 0.21 to 0.28 across strides 36 to 44 -- and identical on all 27
levels. Here the peak is 0.09 to 0.22 excess and moves between levels and
spans, so the two should not be treated as the same kind of claim.

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.