Regarding the number of available codes:

(1) It seems at least one character must be a letter.

(2) Any of the 26 letters may be used, but the numerals 0 and 1 are apparently NOT used, so as to avoid confusion with I and O.

So the number of available 2-character codes is:
(34 ^ 2) - (8 ^ 2) = 1156 - 64 = 1092.

(edited to get disable smilies in place of exponent signs)

[This message has been edited by LastClass (edited 01-17-2003).]