I suspect what you really want differentiation between is P7 PSP and P7 M8; as I recall, the basic differences is that the P7 PSP has a butt-heel magazine release, and that there were at least 2 variants in the configuration of the release lever and the grip plates, and the P7 M8 has the side lever magazine releases, and revised and enlarged triggerguard incorporating a heat shield (of only moderate effectiveness...). Magazines are different between the two main variants as well; I believe P7 M8 magazines, pricey as they are, are more easily obtainable than PSP magazines.
I'm sure others more experienced in the nuances of various P7 variants will chime in. In the 1990s, I personally owned one of the last of the HK P7 PSPs produced for the commercial market, with the final revision of the butt-heel release lever and grip plates, where the release was more streamlined into the pistol's butt profile.
Nice P7 PSP, by the way. It looks like one of the German police turn-ins, by the "NDS" stamp (Neiderschweinstein Police, I believe).