Most of the coins show the normal toning process for mint products. This is mostly due to improper storage. People just don't think when it comes to storing these sets and they typically have WAY too much confidence in mint packaging. Storing these sets is no different from raw or slabbed coins.....MULTIPLE LAYERS OF PROTECTION MUST BE USED.
Hit the cent with some acetone. I don't think I've ever seen something like that, it looks like plastic to me.....which will dissolve in acetone and be removed. I rinse every single proof I get with acetone. Minor surface debris will eventually cause spots! I really hate albums for proof coins, you're just asking for trouble IMO. All of my keeper proofs are in airtite holders as just the first layer of protection. I then use bags, desiccant packs, sacrificial cents and tupperware....remember this:
MO LAYERS = MO BETTA!
Lincoln Cent Lover!VERDI-CARE™ INVENTOR
https://verdi.care/