Hi Dean,
My guess...this gun went back for some arsenal rework after Voglesang retired and Muhlemann was in charge at Bern...??? NO documentation to prove this guess though...
Does the +/M stamp have any "halo" or other bits of white...ie stamped on top of the original finish or is the +/M stamp blued over...???
The "G" and "8" inside the frame would probably just be random DWM inspector stamps used during the original German fabrication...
Regards,
Pete...