Gerben,
It's always great to find that you have something that you didn't expect.
I once bought a handful of Luger and P.38 magazines out of the $10 box at a local shop.
One was a y suffixed Mauser police magazine, and one of the P.38 mags was a very early numbered magazine for a 480 code P.38.
I still have the y suffixed mag and sold the P.38 mag for...

$$