Unfortunately, I’m not very familiar with vintage JLC watches, so would you be able to provide more information about the watch in the photo? The serial number stamped on the back of the case is 85XXX. Am I correct in guessing that it’s from the late 1930...
could be a Frankenwatch, a re-dial, or quite possibly a Corvo Reverso from the 70's (although I don't recall any of them having sub seconds). You'd probably need to send it to Le Sentier to get an actual confirmation it is legit or not.