AN-2-98 to FN-2-98 series

This series has AN-2-98 to FN-2-98 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: 14 APR 98.