Thanks for all your responses.
Yes, for sure I'm not going to just set that one aside. I've only sold one variety that I cherrypicked myself; it was a 1950's
Lincoln Cent with a D/D MM. Even though it wasn't a big deal, I always regretted selling it for just the few bucks I made on it. Nowadays, I keep all the varieties I find in a special place!
One thing that helped in finding the coin with the multiple doubling (tripling, quadrupling?) was that I had been looking at dozens if not hundreds of 1964
Kennedy half dollars for days on end. I got so used to it that was able to look at the lettering on the obverse and tell before seeing the MM if it was a P or D mint! I was fortunate in the last couple of weeks that a relative who had put aside some junk silver in bags for many years gave them to me to dispose of for her, and so, I went through as many as I could beforehand.
One thing I remembered reading in one of Charles' posts about a year ago was the thickening of the letters in a true doubled die. On this one, the thickening was the first thing I noticed which caused me to look more closely. Though I had known that in the past, reading his post reminded me of that phenomenon! There is quite a bit of multiple doubling in "TRUST" of that coin too, but my skills limited the quality of the photos, so I didn't post any.