Testing another family after 3r: could the letters encode numeric data, such as coordinates, phone numbers or fixed-width records? Scripts are numeric.py (code on the baseline task; hashes at the end) and per4g.py, run on N1-r1/N2-r1 (all_tokens.json c9444c80...).
Neighbour dependence. Digit data carries little information from one symbol to the next. In the notes, adjacent letters share 1.25 bits. Letter-shuffled notes reach at most 0.51 (500 shuffles). Independent symbols with the notes' own frequency skew give about 0.10. After cutting out NCBE/WLD/PRSE/SE, the notes still show 1.20 vs a 0.86 maximum. A letter-per-digit encoding of numbers doesn't fit.
Fixed-width fields. By position mod k from the line start, letters are unevenly spread at k=4 (chi-square 123) against a letter shuffle (p<0.005). The effect is mostly E: 53 times at position 0 mod 4 vs 34 expected, 18 at position 2 vs 33. It holds in each note separately. But shuffling group order within lines, which keeps every group intact, leaves only p=0.037 at k=4 and p=0.12 at k=8. With k=2 to 8 all tested, that doesn't survive correction. The periodicity comes from group composition (many short E-final groups), not a field layout.
Phone keypad. Mapping letters to keypad digits gives 3 hits for area codes 314/636/618, vs a shuffled median of 4 (p=0.80). Nothing there.
Clear numbers. 71, 74, 75, 194, 86, 74, 29, 35, 651, "99.84.5", 3 and 1/2 contain nothing resembling St. Louis-area coordinates (about 38.6 N, 90.2 W) as written. That's an observation only; other number formats weren't tested.
So numbers, if present, are in the clear digits, not hidden in the letters. The letter stream behaves like word-like units with strong internal order, which fits the shorthand reading in 3q.
Limits: the neighbour test rules out digit-per-letter codes, but not a scheme where a letter group spells a number word. That would look word-like and isn't tested.
numeric.py 09f117fc42bed73cb01a2b813385a2247311c1a5d43875939f282261825ee8de
per4g.py 8ec4d01fa7031f3fdc30d8c82c88aeb53615ae009525e5c59c2205db77607408