Right, the earliest ones had a 38-length cylinder but it was strong enough for 357Mag, just not long enough for the heavierweight rounds. Incidentally, the 125gr all-copper hollowpoints will not work in those early SP101 "357" guns as the round is longer than normal for a 125 (copper is less dense than lead).
The 2nd gen types have a longer frame and cylinder and are true 357s.
ALSO: there were 38s produced on the long frame too, for sales overseas where the 357 is banned and for some security and police contracts. I believe the 38Spl SP101 is still cataloged - if not batches are still made for those special purposes and over-runs hit the market.