Generally this is true, but sometimes a coin can benefit from removal of foreign substances like glue. You might try acetone. If you use a solvent like that, it can soften up some kinds of glue or paint or whatever. The key is not to scrub them, and to leave the original surfaces and any toning unmolested as much as possible.
Yep. Alcohol can work for lighter deposits of stuff like tape adhesive. Sometimes you need something with a little more "oomph", though. Acetone works well in those situations. But on some stuff like tar, well... that's when it gets trickier.
It happens from time to time. I have seen large gobs of glue on the coins, which made sorting them a bit of pain. If you're lucky it all can be popped right now no issues leaving no residual mess. Nice find!!! ~JobIII
I'm relatively new to all of this. Could someone please tell me specifically where the doubling is in the first three pictures? I don't see anything at all other than the letters being very "deep" for a lack of a better term or they stand out well.