C-0s weren't prototypes. They were developmental steps to the production series. A finalizing step. Not just talking 152Cs, either, but all craft with a -0 series. There were some 100 or so C-1s on a production line at the end of the war in various stages of completion. Not one got out the door, but these were only possible to construct because of the 152C-0.
Ta152 prototypes were not combat craft. The Ta152C prototype, for example, was a modified 190D airframe. The C-0 series was for service testing (including combat testing, how the plane operated, how hard it was to maintain it, to repair it, etc -- the whole package).
A number of the 152Hs that saw combat were H-0s. That doesn't make them prototypes either. They were a stepping stone to what the "standard" would be with the H-1. They were still figuring things out. Normally -0 series (heck, even -1 series most times) don't see combat but because of the rushed nature of the 152's introduction to service in 1945 these ones did.