I have realized a pattern with regards to the last prefixes printed in the initial batch of a new banknote series.
After I learned about BSW being the last prefix of the initial batch of current $20 notes printed, and the same for EKZ on the current $100 notes, and there was speculation that the BSW and EKZ notes were designed as test notes, could it be possible that FEV had a limited number released in the initial batch of Version 2.0 of the Journey $10s printed in 2004 (not 2005) released as replacements, and a higher range was likely used as test notes that were never disclosed?
I feel as if the same thing may have happened with $10 FDY & FDZ, $50 AMH through AML, and maybe some of the $5 HBG prefix. Limited numbers were released of FDY and HBG, but AMH through AML were never released to general circulation (though AMH and AMJ could have been sitting in the vaults, but AMK and AML may have been used as test notes). Could this be possible?