I think the "Made In Purssia" stamp was applied later for import in the U.S. of A. I've done a quick search of my notes and Sauer #92,216 a Model 17 has the "W.B." in a oval as does Sauer #186,309, a Model 40E(the pic is a bit fuzzy though). So it appears "W.B.", possibly Willibald Barthelmes, was the "go to" craftsman when high end frames were needed.

Kind Regards,

Raimey
rse