I believe that Yab is correct on the folder. The steel was still a pretty new material for the maker and the C54 which was about the same time, ended up with warped blades. The reason given was the length of the blades so we stopped making such large blades until the maker became accustomed to working with the steel.
sal
The C-54 big Calypso was the first Spyderco folder I owned made with VG-10 blade steel and I'm certain YAB is right about that one. During that time period there were many of the models made originally with ATS-55 that were converted to VG-10. The Peter Herbst model comes immediately to mind. The J.D. Smith model was originally made with ATS-34 but was converted to VG-10 later.
I would say at this time there are probably more VG-10 Spyderco knives than with any other blade steel. I know that over half of the ones I own are VG-10. It's a great blade steel and I don't look for anything to replace it anytime soon.