Welcome Jeff! And congratulations with a good 'matching' rig!
I was hoping for someone else to answer Q1, I can only quess that it's a acceptance/signature mark of some kind..
It is a quite common mark to find, you may also find an "s" on the frame somewhere on the grip area. Perhaps someone can share some light on it? As to Q2, they where not issued with one matching and one unmatching magazine. Late war, they didn't mark all the magazines. So if it's a proper fxo magazine and aluminium bottom, it's likely that it come from a later byf.
Either way.. you are lucky to have one that actually matches, and both holster, grips and tool sounds 'matching' for your gun. A damn good start at collecting Lugers! ..you will get more of them right?
