The extractor trip pin hole is drilled through the stamping, so that tells you that they appear to have taken receivers at random, but I'm not sure whether the actual number itself was already on or not. What also needs to be understood that SA did NOT assemble rifles in rigid order.

This issue goes back to the trapdoor, and I'm fairly sure that such procedures changed very little. Out of ALL of the "limited production" TDs, ONLY the M1888 "positive cam" rifles had anything even approaching consecutive numbers - EVERY other off beat type spanned thousands (tens of thousands in the case of the M188XRB) of numbers.