The removal of material changes  the  Glass surface not  essential.  The editing  he follows  within the permissible manufacturer tolerances. The permissible  Tolerances  of nominal sizes  are regulated for glasses in standards and processing guidelines.

Here's an example  DIN  EN 572 part 2 called float glass.

There is already  for 8 mm float glass a nominal thickness deviation of 
+/- 0.3 mm allowed.

Typical depths of glass scratches range between 0.02 and 0.05 mm. Sanding out the scratch affects the  Glass surface  not negative.