Trumph serial numbers never included the year in corresponding digits.
I think t100rc means that if the numbers on the bike match the numbers on teh title, forget about any future problems. He's probably right.
http://www.tioc.org/serial_numbers.htm confirms that the letter "S" was never used in the post-69 numbering scheme.
Good, detailed pix will help narrow down the year model, but it's probably a re-stamped "bitsa" made from 2 or more different bikes, and since parts can be mixed from '53 to '83, anything goes.