Maybe I pasted the wrong link. Basically, the date codes break down like this:

The first letter corresponds to the year; since Wilson began date coding in 1968, that corresponds to the letter A, and continues through on a 10-year cycle like so:

A=XXX8
B=XXX9
C=XXX0
D=XXX1
E=XXX2
F=XXX3
G=XXX4
H=XXX5
J=XXX6
K=XXX7

Near as I can tell, the NFL used "I" on 1976 balls, but phased that out when the cycle reset the next time.

As for the second letter, the months count backwards from the bottom of the alphabet, with Z corresponding to December.

O=January
P=February
Q=March
R=April
S=May
T=June
U=July
V=August
W=September
X=October
Y=November
Z=December

Hope this clears it up; thanks for your interest!