I can't speak for those sellers, however, one thing I can tell you is that brand-new S19s still exist, I have them in stock and I sold a few not too long ago to a forum member, of course, your theory is perfectly valid, some sellers would sell a used miner as new, it's not so hard to fake that.
The 90 & 95 TH ones?
I know the 130TH / 140TH are still around as new, but I have not seen any of the 90/95/110 for a while.
With when they went out of production I just can't see the slower ones as new.
-Dave