Why wasn't this caught during printing? I worked for a company that printed newspaper circulars and we had to check the prints every 10 minutes for quality. So

Why wasn't this caught during printing? I worked for a company that printed newspaper circulars and we had to check the prints every 10 minutes for quality. So the department of engraving and printing can't do the same? My theory is that they discovered someone(North Korea?) printing counterfeits of the new bill and are modifying them again.