[Pete] I don't believe Buffet ever had a horn they called "S3 Prestige."  However, there are horns stamped "S3" and these seem to be copper-bodied vesions of the S3.

Anyhow, the horns in this gallery have roller lower C and Eb keys, rather than the patented style from the S1.  You can also compare the rather odd altissimo F# on the Buffet ones to the Keilwerth ones.

I need more examples.  At some point, Keilwerth started doing the keywork for these horns, much like the new Senzo.  A lot of the ones I see under S3 on my old website, saxpics.com, are Keilwerth-keyed.