There was no SPC.

The SP3 was the last of the 916cc engined SPS. It wasn't a 955. It was made that you could bolt a 955 kit straight on though.

The 916SPS was the first of the 996cc engined ones I believe although not totally sure about that. I believe that there was a 916 one in 1997 and a 996 one in 1998.

The 955SP is a rarety that was just made for the US homologation. 50 of them produced. Nothing utterly special though, just a SP with 955 kit.