I had just bought 2 1970 proof sets, and was going through the cherrypickers guide to see if there were any errors. For some reason, I looked at the back of the cents, and there is a definite difference in the UNITED STATES OF AMERICA. The "United" seems unevenly spaces, and the AM in America has but a paper width seperation, where as the other has a definite seperation. I've checked some 1971 proof cents, and they all have the seperation. Has anyone heard or know of this as an error coin?