yes - Ultimate had a fairly distinctive seat collar - that frame doesn't and you can see top part of the ST has been replaced - notice the bulge about 4" from the top?Is it possible to see that from the pictures?
see attached versus what it would have looked like.Is it possible to see that from the pictures?
I think you might be right actually!Is that not just the design of the later frames?
I seem to recall from '93 that the independent collar had been dropped in favour of an integrated pinch bolt, can't see why that wouldn't have been applied to the Ultimate.
Edit:
Pinch bolt visible in '93 Catalogue
https://www.retrobike.co.uk/archive/1993-yeti-catalogue.49/download