Based on the photo of BYF 41 serial number "6241z" by Tharpo (Much appreciated!), and the remarkable similarity of the number "6" digit stamp, I will revise my opinion to say that my suspicions have been neutralized, and I feel that this frame has not been altered. Alanint has called it... a bad day on the production line, and nothing more. The number 6 stamp evidently "bounced" when the hammer struck causing the shadow image.

Thanks to all for your detailed evaluations of this piece, seems like it was educational for more than just the original poster...

I looked it over very close I think I din't get the best angles for my pictures. I using my cell phone and try to take the pictures on a angle so the numbers show up. I just figured if someone was going to go through all the work to grind and restamp the frame he would grind off the excess on the slide groves. They don't look out of place to me. The guy I got it from was a WWII vet and said he had it a long time but din't bring it back. So if it is altered it was years ago before Luger's were as popular as today

The holster code CEY stands for

Karl Budischovsky & Sohne, Osterreicheissche Lederindustrie AG, Vienna.

(The Standard Directory of Proof Marks, German ordinance codes - Gerhard Wirnsberger - a Green paperback)

Thanks for all the information I was a little worried about its authenticity I paid 2,200 so I had a reason to worry. I know its hard to really evaluate without having the pistol in hand. Thanks again for all your time and effort you gave me. John