The article I read said that the coins in question where accidentally minted without In God We Trust, and that some where released without a date on them. They have been according to the mint selling to collectors as mint errors.

One can also sometimes find bills without serial numbers, or mint seals, sometime bills are issued that have no printing on the back, or coins that are struck off center. You can find them on ebay, and at coin shops. They usually sell for more than the face value as they slipped past the inspectors who may have been tired, lost focus, or been thinking about the next bathroom break.