The combination of "Made in Germany" and Austrian NPv or NPf proofmarks is not unusual. In fact this alone dates a gun to 1938 – 39. After Austria was annected (with much applause by many Austrians, a fact now forgotten by them) by the 3rd Reich on March 12, 1938, not everything changed immediately. A new German proof law was already worked on. So the former Austrian proofhouses, Vienna and Ferlach, continued to use their procedures and stamps until the new, 1939 law, proof rules became valid on April 1, 1940. The .39 date was not applied by the Steyr factory, but by the proofhouse. Only from then on guns made in former Austria were marked with the German eagle/N proofmarks and the German month+year dates. So your rifle was not sitting in stock, already proofed, since the 1920s, but was assembled and proofed in 1939.