You're lucky to have gotten to meet him and have things signed, an opportunity I never had. Better hang onto that one, that's a pretty neat error. If you look close, you can see where he stopped the pen for a second before they "y" as if to say "Oh, there should be an "e" there... ah, whatever..."
And 100 Mick signatures??? WOW. If I'm ever in PA, I'd love to see your collection.