Bear in mind that a clear coat has a thickness of 1.5 – 2.0 Mils, removing more that 0.3 mil
(0.0003-inch or 14 µ) of clear coat will cause premature paint film failure. As a point of reference two sheets of Saran wrap placed on top of each other measure 1.5Mil (0.0015") a surface scratch that will `catch' your fingernail is approximately 0.003-inch - 14 microns deep and will usually require wet sanding and refinishing.
There comes a point when you must judge wither removing a scratch will compromise the clear coat and if so you’ll have to ‘live’ with the imperfection. Check the paint with a PTG to see how much paint there is available before attempting repairs Clear coat that is too thin looses its ability to adhere effectively (delaminating) to the underlying paint layer and will flake off
For our British readers-
Comparison between millimetres and microns; a Mil is equal to 1/1000 of an inch which can also be represented as 0.001- inches or 0.0254mm (mm = millimetre). A micron is equal to 1/1,000 of an mm or 1/25,000 - inch or 0.00004- inches. There are approximately 25 microns to one mill (0.001- inch) Microns to mils: divide by 25.4
Sorry Dave couldn't resist as I know you teach physics