I put all of my nicer coins in 2x2s, even if they're only worth a few cents.
Judging by your other posts, your grandfather seemed to know the basics about mint errors. If he thought this coin was an error, he would have written something about it on the 2x2.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis