Every US banknote has two serial numbers that should be identical. A mismatched serial number error occurs when these two numbers differ — one or more digits are different between the upper and lower (or left and right) serial numbers on the same note. This error happens when the numbering wheels on the overprint press malfunction, and it produces one of the most collectible and verifiable currency errors.
During overprinting, two separate numbering heads simultaneously print the serial numbers on each note. If one numbering head's wheel sticks, skips, or advances incorrectly, the two serial numbers end up different. The mismatch can be as small as a single digit or as large as a completely different number. The more digits that differ, the more dramatic and valuable the error.
Value depends on how many digits are mismatched and by how much. A single digit off by one (e.g., serial ending in 5 vs 6) is the most common type and typically sells for $100-300. Multiple digit mismatches, large numerical differences, and notes where the entire serial differs are significantly more valuable. Denomination, series, and condition also affect pricing.
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Scan NowThey are uncommon but not extremely rare. The BEP's quality control catches most, but examples do enter circulation regularly enough that alert collectors find them. Single-digit mismatches are more common than multiple-digit mismatches.
Carefully compare both serial numbers on your note, digit by digit, including the prefix and suffix letters. Good lighting and magnification help. Even one digit difference constitutes a mismatch error.
A stuck digit occurs when one numbering wheel on the overprint press stops advancing. This causes one digit in the serial to remain the same on consecutive notes while the other serial advances normally, creating mismatches.
For single-digit mismatches on common denominations, grading is optional. For multi-digit mismatches or mismatches on older/higher denomination notes, professional grading adds significant credibility and value.