Some common currency printing errors include inverted or blank backs, overprints, upshifts and double currency printing. Inverted backs are a common occurrence and result in the reverse side of a note being printed upside down in relation to the front.
Blank backs occur when there is no printing on the reverse. Overprints occur when the front and back get struck on the same side of the note. Upshifts are simple misalignments in which the notes are printed outside the cutting parameters of the paper stock. Double currency errors occur when the front of a note has one denomination printed on it and the reverse has a different denomination. Some other common errors include ink smears, mismatched serial numbers and overstriking that occurs when the same side is printed twice but is slightly misaligned.