Serial numbers seem to be one of the most common production oddities/errors found and it most likely started on the very first bikes that came with the hand stamped serial numbers.
The machine stamped serials started a whole different page on oddities or errors that were caused by both mechanical and human error. Many believe the serial numbers were stamped when the frame was built, and that may have been the case decades ago until the manufacturers realized it was more efficient to pre-stamp the numbers on the actual part before it was used in building a frame.
Pre-stamped serial located in the wrong location. The 1960's Tandems used electro forged dropouts to the chain and top seat stay and the middle stay was hand welded to the dropouts and those welds covered part of the serial numbers on numerous pieces.
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A 1970 Schwinn Twinn with a serial stamped on the dropout and one stamped on the head tube. This tandem was built with two pre-stamped components during the change of the serial number location in 1970.
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At the beginning of the January 1966 stampings there was either a mechanical issue or possibly someone failing to insert a stamping die in the stamping head. Someone didn't check the stamping dies in the machine so some were stamped with no year letter and some were stamped with no month letter. This is noted on the Anglefire serial list as
recorded in error, but it was actually a
stamping error.
1966 Varsity missing the year stamping die.
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