Here @ HKPro is the best place to find out.
From what I have learned, the SS slide was an option on all the USP full size 9mm, .40, and .45. It was also an option on the compact 9mm, .40 and .45. There were no tacticals, compact tacticals, elites, or experts in SS.
It was also an option for the USP Matchs, the most common being .45. AFAIK, there were never any 9mm Matchs imported but a few made it in. All the ones I have seen were SS. I have also seen a few in .40 that were SS.
Also, all SS were black frames. There were never any with the green, tan, or grey frames.
Variants are the same as any USP, only difference was the slide was made out of SS. There was also a run in the mid 90's for a matte SS. I think the only date codes for that were KG and KH, IIRC.
And here's a few of mine.
http://www.pnwzj.com/images/6hks.jpg
http://www.pnwzj.com/images/usp31mag.jpg