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I've got one of those too. It's a real beauty. It's one of the primo "A" series. Not that there's anything shabby about the "C" and "C N" series - they're also very fine. AFAIK, there are no "N" versions of the A 120/4 Macro M, A 200/2.8 APO, A 300/2.8 APO, and A 500/4.5 APO. I have the A 120/4 Macro M and A 300/2.8 APO.
Actually, those are all N-only lenses, there's no C or S versions of them. The N lenses are the last series of Mamiya lenses and all of the APO lenses are N (IE they have N barrels and coatings which are the primary differentiation between N and earlier lenses). As far as I'm aware, the A only refers to them being APO designs, otherwise they part of the N series.