The “PZM” name was attributed to S&B’s Factory at Schoenebeck am Elbe, from about 1939 to 1945, during which time it was given both a “P” number and then a Letter code.
The Use of the “Commercial” designation would indicate NON-Wehrmacht supply (Probably Police or SS) as was common up to about 1942-43, when all Non-Wehrmacht entities then got access to “Military” marked German Ammo.
It is interesting to note that the accession of Albert Speer to the Munitions Ministry co-incides with the change over of supply arrangements for the SS etc. Speer improved a lot of the chaos which was occurring in Germany’s Munitions supply arrangements in the early years of the War, but as usual with Germany’s War Effort, a lot of innovations were “too little” or “too late” or Both.
A bit of cross-Historical reasoning.