John Adams Presidential Dollar Errors (coins.about.com)

It should come as no surprise to coin collectors that some mint errors are being found among the John Adams Presidential Dollars, which were officially placed on sale this past Thursday, May 17. I've had a scattering of reports, most of them minor, and some of them recurring on the reverse in the same fashion as they are known for the Washington Presidential Dollars. However, I have one report of a major error on the Adams Dollar: A double set of edge lettering! Judging by the photos I have seen, (which I hope to have permission to post here later today,) the coin went through the edge lettering machine twice, with the lettering oriented in the same direction each time.

At least five specimens are known of the double edge lettering on the Washington Dollar, which makes this error exceedingly rare considering that the mintage was around 300,000,000 coins. . . .

Full story at:
http://coins.about.com/b/a/000113.htm