"I too have my own repair number system, and a label gets stuck on the unit
with the date and repair number on it."

Y'know, those could be done by the folks who print custom bumper stickers.

Commercial mirror adhesive hasd a spray to spray on the windshield before you apply the glue. This stuff applied aforehand, on metal or plastic is likely to make it unremovable period.

Of course, do you have the right to do that ? If I pay for a premium repair, don't I have the right to have a repair that is undetectable ? If I cannot stick my sticker on the fornt, what gives me the right to stick it on the back ?

I agree with you, that we need to mark these units because I have seen people try to pull this ****. But where do you draw the line ?