The A could just stand for what bin the carbine was stored in. Not much information about the painted rack numbers being found.
here's a interesting link to a OI Inland stock that came with a label taped under the forearm.
A member of another forums wife passed along the information about it.
Cheers,
Charlie-painter777
Korean markings,
Korean (?) ID Tag on Carbine Stock - Page 2 - Military Surplus Collectors Forums