Did GM shim starters from the factory?

If they didn't shim starters from the factory which I've never seen this then why do new starters need to be shimmed? Ford and mopar starters do not the shims.

Ford and Mopar use starters that were bolted into the flywheel GM was bolted up to the flywheel. The starter bolts would come loose or break and it would cause the starter to move around causing wear on the aluminum housing. If you had a worn housing and not shimmed the clearance for the starter gear to the flywheel would be to tight and it would break the bolts.

My 82 C10 had shims on the starter.

Hi so as we have no idea what is you are going on a about some explanation is required.