To date the assembly from the barrel code, you need either 2 or 3 letters, since "K", by itself, could indicated the month or the year.
Month codes:
B = Jan
L = Feb
A = Mar
C = Apr
K = May
P = Jun
O = Jul
W = Aug
D = Sep
E = Oct
R = Nov
X = Dec
Years that "K" has been used as the year code:
1941, 1963, and 1990
Jeff