The last letter advances through the alphabet when all eight character serial numbers have been printed for a specific Federal Reserve Bank within the same series. The first letter of such a serial number identifies the Federal Reserve Bank (FRB) which issued the note since there are 12 FRBs, this letter is always between A and L. Up through Series 1995, all Federal Reserve notes had serial numbers consisting of one letter, eight digits, and one letter, such as A12345678B now only the $1 and $2 notes still use this form.
Each note of the same denomination has its own serial number.
