There have been a few Rolex clasp code formats over the years all between 2 and 5 characters long and made up of numbers and/or letters and perhaps a dot. The longer number is a type code and not covered here. Clasps stamped USA are also not covered yet. If the date of the watch is very different or if the clasp type was not being manufactured during the year suggested it tells you that further investigation may be required. During the early to mid-70s there was a gap where no datecodes were used at all. You may find your code is split across 2 lines, if this is the case enter it all on one line but do include any dots used on the clasp so :-
Should be entered as 4.65
If your clasp has an 'S' spaced slightly away from the rest of the code then this indicates it is a replacement (service) clasp, please remove that S when entering the number here.