{
  "schema": "gearbox-reverse-revision-evidence-v1",
  "scope": "Two separately documented reverse-gear changes; no fitted configuration or working tooth geometry selected.",
  "factory": {
    "publication": "British Leyland Austin MG Technical Service Bulletin75-D-4",
    "date": "March1975",
    "source": "https://www.chicagolandmgclub.com/techtips/tsb/TSB_no75d4.pdf",
    "sha256": "d567a6e3812ad5635b4a8ded3e80bd0b391a950290e21e46824f3431c9298bbc",
    "read_scope": "Single-page original bulletin visually read after normal public download returnedHTTP200.",
    "body_roles": "Mainshaft reverse gear and laygear leading edges change from pointed to rounded to reduce chipping.",
    "midget_gearbox_number": 2270,
    "marina_context": "18V272621; retained separately,not a Midget identification threshold.",
    "part_number_rule": "Bulletin states unchanged numbers and individual interchangeability for this tooth-end modification.",
    "nomenclature_boundary": "Heading names mainshaft reverse idler; body says mainshaft reverse gear. Do not infer that every component called reverse idler in another catalogue changed under this bulletin.",
    "not_supplied": "No tooth counts, nose radius, helix, dimensions, installed variant or repair sequence."
  },
  "supplier": {
    "publication": "Moss Europe Sprite/Midget catalogue Issue25",
    "source": "https://www.moss-europe.co.uk/content/files/pdfs/moss-europe-sprite-midget-catalogue-issue-25.pdf#page=205",
    "sha256": "13a3ef5c108a955218a02fcfd1c221af62842f1da2ff1dd2944204a46237d9c8",
    "pdf_page": 205,
    "printed_page": 147,
    "read_scope": "Gearbox147 page image visually read; only listing-change and matched-set note used.",
    "early_through": 241363,
    "later_from": 241364,
    "listed_sets": {
      "early": {
        "synchro_1_2": "156911WO",
        "laygear": "22G1818",
        "reverse_idler": "144580"
      },
      "later": {
        "synchro_1_2": "DAM6828SR",
        "laygear": "DAM6475",
        "reverse_idler": "DAM6826"
      }
    },
    "conversion_rule": "Supplier describes these three as a coordinated specification change requiring all three when converting to the alternative.",
    "limits": "Supplier application/cross-reference,not the1975tooth-end bulletin or proof of fitted internals. No bearing,oil,overhaul or replacement instructions from this page are adopted."
  },
  "interpretation": "Different changes with different identifiers and scope. Neither model year,nor the engine number,nor an unchanged service part number selects fitted reverse-tooth form or the coordinated gear set. The bulletin individual-interchangeability statement is not generalized to the supplier later-set conversion.",
  "model_action": "No CAD or placement changes. The laygear/input/reverse roles remain simplified; existing mainshaft catalog tooth counts do not identify the mating set. No radius,count or operating mesh is invented.",
  "remaining_dependency": "Fitted gearbox identity,component markings and actual reverse/synchro configuration remain unverified. No new owner capture is requested."
}