I think @Publius2 was on the mark. It probably would have been 64 if it didn’t have that rim dimple on the reverse.
Presumptively it was dipped at some point. Not taking anything away from it, but they just don't age like that. These days, almost all blast white silvers that grade have been dipped, at some point. Were it dipped, it was, as the market considers, an "acceptable" dipping. I'd have given it a MS64, Randy. But then I'm a sucker for blast white silvers. Handsome coin.