Correct, shimming a mount is useually done to compensate for wear on the lens flange or PL mount, to reset it back to correct FFD. If a lens is correctly collimated for the PL standard, you are good to go.
EF mount is another story, it is not precise enough, and actuall Camera FFD May vary from one camera model to another. Also, some zooms need the back focus reset to get it parfocal. But again, a correct collimated Cine Zoom should be parfocal, if the Camera Mount FFD is correct.
One way to tell is to have two cameras, with the same mount set to the same distance on a kens test chart/target put the lens on camera A set what the witness marks lines up to, then put the same lens on camera B and check again. If both are set to correct FFD, witness marks will be the same, hosever with some less expensive lenses, the distance scale may not be completely accurate, and may not indicate the actual distance.
Another test is to rent a a Cine Prime, like a Zeiss Ultra Speed (if PL) or a CP2, and test the lens on the camera at say 6-feet, check the witness mark, it should be close to 6-feet, the backup to 10-15 feet to line up with the next witness mark. If the distance shown in the lens is less than the actual distance, the mount is shimmed too far out, remove the 0.010 shim and try again (lens will not focus to inf. If the distsnce indicated is further away, (normally the issue with EF lenses, so they focus to inf. on a variety of cameras) then add a thin shim, and recheck.
The most accurate way to test the camera mount FFD is with a collimator for the lens mount (EF or PL) put it on the camera instead of the lens, turn it and the camera on, and see if you get inf. Focus. Wooden Camera has a video with their MF/PL Pro adapter listing thst shows how to do this:
https://www.woodencamera.com/mft-mount- ... 233500.htmCheers