Docs: E-IV bank interiors are read, and have been since D14

README.md

@@ -122,7 +122,7 @@ These discs are also the only place in this project where the correct output is
 - **Roland S-550, Ensoniq and Kurzweil filesystems.** `Roland LCD1.iso` opens `* ROLAND S-550 *`, which shares nothing with the S-7xx format ([ADR-0014](docs/adr/0014-one-backend-per-on-disc-format.md)); neither archive holds a second specimen to check a backend against. The container layer opens all of these, so `export-iso` gets you the sectors meanwhile. Each backend is a self-contained module ([ADR-0003](docs/adr/0003-brand-neutral-pluggable-backends.md)), so adding one touches nothing else.
 - **Roland S-7xx discs come out as one flat volume.** The disc groups its samples through a volume → performance → patch → partial chain, and two of those four record formats are undecoded, so every sample is listed under the disc's own label instead. The four-character prefix in each name is the grouping you get ([ADR-0016](docs/adr/0016-the-s7xx-hierarchy-is-located-not-walked.md)).
 - **Roland S-7xx sample rates are written as 44 100, not read from the disc.** No rate field has been found, and pitch cannot settle 44 100 against 22 050 because they differ by exactly an octave. Every disc measured is 44 100; a 22.05 kHz one would come out an octave high ([ADR-0018](docs/adr/0018-the-s7xx-sample-rate-is-measured.md)).
-- **Emulator IV bank interiors.** E-IV discs list their folders and banks correctly — the directory is shared with EIIIX and ESI — but the inside of a bank is a different layout with only one specimen to hand, so those banks are listed and not extracted ([ADR-0015](docs/adr/0015-locate-banks-by-signature.md)).
+- **E-mu `E4P1` presets are not read, and some Emulator IV banks have no sample directory.** E-IV bank interiors themselves *are* read — through the chained `E3S1` sample directory rather than a bank header, since those discs carry none ([ADR-0020](docs/adr/0020-read-e-iv-through-its-sample-directory.md)). What is left is the presets, which hold the key ranges and envelopes: the three E-IV discs carry 916, 901 and 284 of them and nothing parses one. On `Studio Essentials`, 100 of 230 banks have no confirmed sample directory and are listed with a note rather than guessed at; preset-only banks are the likely explanation and it is not established, so it is not claimed.
 - **A `.mds`/`.mdf` pair is read, but its descriptor is not parsed.** One pair has now been through it end to end, and it reads the `.mdf` and sniffs its geometry rather than parsing the `.mds` — correct for a single-track data disc, which is what these are. A multi-track or offset image would be read from byte 0 and come out wrong; the track table is unread. Please open an issue if you have such a disc.
 - **`CUES` chunks in NRG** are not parsed; only `CUEX`. No disc using the older form was to hand to check the layout against.
 - **An audio CD with no cue sheet cannot be split into tracks.** `samplerdisc info` tells you when a disc's content looks like Red Book audio, and `extract --assume-audio-cd` writes the whole stream as one WAV, but the track boundaries live in a cue, not in the bytes.