Here’s what they really mean:
F: First Class
A: First Discounted
P: First Class Premium Upgrades
O: First Redemption/Regular Upgrades
C: Business
D: Business Discounted
Z: Business Discounted
J: Business Class Upgrades
I: Business Redemption
Y: (Unrestricted) Coach Class
B: Revenue Coach Class
M: Revenue Coach Class
H: Revenue Coach Class
Q: Revenue Coach Class
N: Revenue Coach Class
V: Revenue Coach Class
W: Revenue Coach Class
L: Revenue Coach Class
S: Revenue Coach Class
T: Revenue Coach Class
G: Revenue Coach Class
K: Revenue Coach Class
U: Revenue Coach Class
E: Revenue Coach Class
R: Revenue Coach Class
X: Coach, Frequent Flyer Redemption