johan, you are right.
even after the war the "DRP" appeared on the top plates - there was no patent administration office after the war, so only the old prewar patents applied (they were annihilated anyway - opening the road for russian and especially japanese manufacturers).
even later the federal patent offices were installed, leading to "DBP".
there should be some more detailed articles on the net, maybe in german, but since i just cannot remember where, for the moment i do not start researching. please forgive my laziness.
cheers
sebastian