That's a pretty bad obverse spot . Not sure about corrosion but nasty . As mentioned it's a brilliant proof not Cameo , you will know a Cameo when you see one . I'm thinking this could be a Proof Details coin although I don't think I've ever heard of one with that designation . If by chance that's not corrosion ,then I'll say PF-62 .
Give a man a fish and you'll feed him for a day . Teach a man to fish and you've fed him for a lifetime .