The commonest marriage is the pocket-watch movement recased as a wristwatch — a trade that grew as pocket watches lost value and large wristwatches became fashionable. Tell-tales include a wristwatch case whose size matches a standard pocket-watch calibre (16 or 18 lignes and up), a dial with the small-seconds position of a hunter or open-face pocket layout, and a crown position that does not match the movement's original stem placement.
Period recases are different from modern marriages. Watches were legitimately recased in their own era — a gold case scrapped for its metal, a movement moved to a newer case — and a documented period recase is part of the object's history. The problem is the modern assembly made to look original, which misrepresents both parts.
Check the witnesses against each other: movement serial date, case hallmark date, dial style and hands should all belong to compatible periods. A 1910 movement in a case hallmarked 1935 with a 1950s-style dial is three objects, not one. Mismatched screw marks, extra case screw holes, and a movement ring or spacer where none should be are physical evidence of adaptation.
Dials deserve special care. Repainted dials are common and often well done; look for printing that sits on top of aged lacquer, signatures that do not match known factory styles, and lume that glows where radium or tritium should have died. A refinished dial is not necessarily deceptive, but it must be disclosed to be honest.
Cataloguing an assembled watch honestly costs it little and protects everyone: 'movement c. 1912, later case, refinished dial' is a saleable, study-able description. The damage is done by silence — an undocumented assembly enters the record as a false original and corrupts every comparison made against it afterwards.