Serial Number Errors: Mismatched, Misaligned & Inverted Serials

Every US banknote carries two serial numbers that should be identical. Serial number errors occur when these numbers do not match, are printed in the wrong position, or contain other anomalies. Because serial numbers are applied during the third printing stage (overprinting), errors at this stage produce distinctive and collectible varieties.

What This Means

Serial numbers are part of the "overprint" — the third and final printing pass that also applies the Treasury seal and Federal Reserve seal. Serial number errors happen when the overprint plates are damaged, misaligned, or when mechanical problems cause inconsistencies between the two serial number printings on each note.

What to Look For

• Mismatched serial numbers — the two serials on the same note differ in one or more digits
• Inverted serial numbers — one serial appears upside down relative to the other
• Misaligned serials — numbers shifted up, down, left, or right from their proper position
• Missing serial numbers — one or both serials partially or completely absent
• Overinked or underinked serials — numbers that are blurred, bold, or faint
• Partial serial numbers — numbers that start or stop mid-digit due to paper position

Common Mistakes to Avoid

• Not comparing both serial numbers on each note — mismatches are missed if you only check one
• Confusing wear-related fading with genuine missing ink on serials
• Assuming any unusual serial (like repeating digits) is an error — unusual combinations are not errors
• Not distinguishing between misaligned overprint and misaligned cutting
• Washing or chemically altering serial numbers — any alteration is illegal

What Affects Value

Mismatched serial numbers are among the most valued overprint errors because they are dramatic and easy to verify. The extent of the mismatch matters — a single digit difference is worth less than multiple digits differing. Missing serials, inverted overprints, and dramatic misalignments also carry strong premiums. Condition and denomination affect pricing.