My Walther P-5 is a German BMI trade in from SOG too. Mine is dated 2/84 and I bought it from SOG about two years ago for around $ 375. $ 450. is an OK price. You will find the BMI marked lined out on the left side of the slide to the left of the S#. PW Import mark on frame forward of the trgger under barrel. It is a very nice pistol and I like it very much and will not think of selling it even though it is a 9mm. I am a Colt 1911 45 ACP type of person, but also like Walther PPK/PP too.
Great gun for a very good price, I love it!
Also "BMI" is the Federal Interior police, old border guard ect.