I received a $20 bill that appears to my inexperienced eye to be legit, watermark and all. It is the same width as a regular 20, but as these pictures will illustrate, the top margin is small, the bottom one is too large. It is 2004 A GK23421115C worth anything?
The BEP does not consider it to be an error until the design actually touches the edge of the paper. Even then, a portion of the design needs to be missing for it to fetch a premium.