Just bought a rusty ol' Trek and through different measurements I'm guessing it's a Trek 910. Components are a mix: lots of 1st Gen Dura Ace, Ambrosio Champion bars, fluted Mavic stem, random campy accessories.

I've tried to date it, but am coming up short. It looks like some previous owner sprayed black spray paint on the bottom bracket shell. I can't see any serial number anywhere. I started sanding to see if the serial number would eventually surface, but now I'm getting nervous. I've sanded super slow and checked often for any signs, but I'm down to bare steel. There's a bit of a flat spot in the shell that I know I did not sand away, and I'm worried that this was stolen at some point and the thief sanded off the serial number 😭.

Should I keep sanding? Stop sanding? Look elsewhere for a serial number?