In my city I have trouble buying stuff without a serial number from a watch. I'm guessing this didn't happen to you?
I sent an email saying I had an old seamster with same size bracelet, and wanted to upgrade the clasp to the new adjustable type and I have been told it is a direct replacement. They did not ask me for anything else.
I do think it depends on who you end up talking to. I have ordered rolex parts before in the same store, one salesguy took the order without hesitation, the other said I would have to bring the watch in to verify what I am asking is the correct part.