AN-6-96 to FN-6-96 series

This series has AN-6-96 to FN-6-96 printed in the lower right hand corner, followed by either a blank,
or a series of letters always starting at "K" then descending in sequence to "A".
Once "A" is reached, a series of numbers always starting at 0 (zero) then descending in sequence to 1 follows.
Earliest known date: 23 MAR 97.