smith and wesson

i have two pairs of smith and wesson 100 cuffs one says springfield mass and has pat pending the other says houlton me and has m-100 the first pair dont.
i was told the second pair was older but just wanted to know if anybody knows anything about them as when i emaild smith and wesson they say they dont keep records. if any body knows the age that would be good as thats what i want to know thanks martin

Some clues:

If one of them has the "double-lock slot" on ONE side only...then, that's the earlier (first) model.

"Springfield" is earlier than "Houlton".