Revolvr,
you might be right about the extractor in picture #17. I looked at about 10 of my artilleries and I only found one that didn't have a serial number on the extractor and it was also a 1917. I know my gun is legit. Even two other 1917's of mine, a 1918, a Thai artillery and a bunch of others had serial numbers. Maybe a person on the German assembly line was doing some singing

and missed it.
Big Norm

<-- I'm singing!