I think JP Sauer always put their name on their guns, but I could be wrong. In any case, all those German doubles are pretty much the same. I doubt that Herr Klavberg was actually the maker; he was probably a retailer selling trade guns turned out by a guild or sort of a gunmakers' co-op.
A picture of the proof marks would tell if the gun was made before or after WWII, and also if it was made in Kiel. The Kiel proofmark looks like a kind of sunburst superimposed on a "Y"; any other mark would indicate the gun was not made in Kiel. (Technically, a maker could have his guns proved at any proof house in Germany, but in practice the nearest was always used.)
In Germany and England, it was common for the actual maker(s) to leave the barrels blank so the retailer could have his name engraved or, sometimes, to engrave the retailer's name at the factory.
It is not done so much any more, but we used to do that here, with guns and other products. Remember guns "made" by Ted Williams and J.C. Higgins?