What is it?

[Edward Tinker]

I have never seen a mag safety luger without a sear safety that matched

I have many times seen sear with mag or sear without mag, but never a mag without a sear

If matching, I would expect that the hole for the sear is there (if no safety) - if sideplate is not cut, then it is a replacement sideplate

This is why a complete gun, showing serial numbers matching is important.