Resin printer build plate scratches/ damage
One of the resources I've found is a forum with a discussion of the impact of scratches.
The general consensus is that scratches are not a problem, as long as there are no burrs above the surface of the plate that would damage the bottom of the vat. One posting party has used 36 grit on a palm sander followed by scotchbrite pad to resurface his plate, but one takes the risk of creating an out-of-plane surface.
A better method to sand a plate would be to place the sandpaper on a glass surface or something equally flat and planar and pass the build plate repeatedly over that.
Another aspect of the discussion was that scratches are good, as the rough surface provides a better bond to the resin.
You're likely to note that your build plate is not a polished smooth surface for the same reason.