backlog: S18-S23 settled, S17 confirmed absent, GP_TUTORIAL.pak refuted

docs/re/BACKLOG.md

@@ -900,9 +900,23 @@ the route-name kind letters `F/S/A/M/B`, what activates a sub-objective, and
 durations, spawn triggers and arrival positions are not in `UnitGroup`. The
 stage record names two untouched candidates: `Formation_*.tbl` (formation
 geometry, possibly its timing) and `EnumSquadron_Test.tbl`. Also still open: the
-4-byte record key, the member field `n`, and the missing S17–S23 stage records
-(S17 has no `UnitGroup_S17.tbl` either, so the whole stage is absent from
-`GP_MAIN_GAME_E.pak`).
+4-byte record key and the member field `n`. ~~the missing S17–S23 stage
+records~~ — **SETTLED 2026-08-25, and half the premise was wrong.**
+* ✅ **S18–S23 stage records were never missing.** `stagetbl.py Stage_S18` returns
+  a full six-record definition and always would have; it was never run. They omit
+  the literal `Stage_S<NN>` (no per-stage `.xpr`; `AIParams`/weapons/strings/
+  subobjectives/nameplate/collision all come from a shared **`_Tutorial`** set),
+  so an enumeration keyed on that literal skipped all six. Counting distinct
+  `*_S<NN>` names across all **1119** decompressed entries: `UnitGroup` and
+  `Route` cover **28** stages (S01–S16, **S18–S23**, S24–S29); `Stage` literal and
+  `AIParams` **22**; `SUBObjectiveSettings` **16** (story only). Tutorial records
+  carry the same `Phase_1/2/3` shape, so the tutorial is not a special mission
+  type at the data layer. Dump in `data/stage-tutorial-records.txt`.
+* ✅ **S17 alone is genuinely absent** — it appears in *none* of the five families.
+  Not a stage that lost its data; it does not exist. Matches the family split in
+  `challenge-mission-gate.md` (story 1–16, tutorial 18–23, challenge 24–29).
+* 🔴 **Refuted:** `GP_TUTORIAL.pak` does **not** hold the tutorial stage config —
+  2 entries, both RATC, zero IDXD, exactly like `GP_CHALLENGE.pak`.
 
 ## The dynamic-RE state is not in git, and it was gone