ADBP:
Just guessing, but I'd say the Lifetime warranty would only be good to the original purchaser..
The only manufacturer that I'm AWARE of that offers a "forever", no questions asked to owners of their firearms, new or used, original owner or number 45 is HiPoint..
I WOULD guess that if you bought a S&W firearm used and something related to a factory defect caused it to quit functioning properly you would have a case for getting it fixed free with S&W Customer Service.
Several years ago I bought a "like new" (but NOT new) Colt Detective Special. I couldn't hit the broad side of a barn, from the inside, with it, and having 2 other D frame Colts (Cobras) to compare it with, plus several J frame Smiths it was obvious the DS was somehow out of whack.
I called Colt CS and they said to send it in and they'd evaluate it and let me know how much it would cost to fix it.
I paid for shipping TO Colt, but when the little DS came back the shipping was prepaid, and there was no charge for the repairs. Turns out it was "out of timing" or something, and they fixed it, PLUS smoothed out the da trigger pull, as a "customer service"..
I think Smith would do the same with a firearm, even used, that had a problem that could be traced to a defect from the factory when new.
IMO Smith & Wesson has one of the best Customer Relations Departments in the firearms business.
FWIW, 3rd Gen Smiths are built quite well, and I don't think you'll ever have a problem with it unless you somehow abuse it.
Best Wishes,
Jesse