By the resurge of the P151/dnf I talked to a few fellow collectors.
They pointed my attention to P334/fb Mansfeld A.G., Plant Rothenburg/Saale
They used 2 different machine streets for the producing of 7.9 Mauser rounds.
For error identification they marked the head stamp. It was known that the “fb” head stamps exist with and without a dot behind the factory code.
The way they made the head stamp of the material code was not noticed by me as identification of the production line.