Scotch Tape Residue On A Proof, Acetone Did Not Remove.

Has anybody even noticed the damage on the rim from the heat pack sealing machine?

EDIT: Don't mind me - sometimes senility creeps up on me!

If you are keen to experiment, sure. But otherwise, yes, time accept it or look for a better example.

Mate bought a new stainless steel spatula today and an adhesive label was attached to it. The label mostly peeled off but left a sticky mess behind. Hot water and rubbing with my finger just moved the adhesive around. Rubbing with a paper towel soaked with Windex was equally ineffective. A paper towel soaked with 91% isopropyl removed it with much effort. The next step would have been WD-40. Glad this wasn't a proof half dollar.

There is something to be said for collecting old coins which are never expected to be perfect (though I can also appreciate the attraction to perfection)

Well, this coin is still in the acetone, still with the surface haze, waiting on the next move. In researching proof Kennedy half dollars with collar clashes, I turned up only one other legit example (a 2000-S on Reddit), so I really don't want to foul up this error coin.

I have 91% isopropyl alcohol from a pharmacy. Are there concerns that it might contain contaminants or additives? If anything will show a problem, it would be a proof coin surface. Maybe xylene is a safer bet?

I agree. It should be fine, but you can test it. Place some in a really clean glass bowl and let it evaporate. If there is no residue on the glass, all is good.

Any further results with the adhesive/haze?