Revenue buckets
J - Full Fare Business
C - Discount Business
D - Discount Business
Z - Deep Discount Business
P - Deep Discount Business
O - Full Fare PremiumPlus (Premium Economy)
A - Discount PremiumPlus (Premium Economy)
R - Deep Discount PremiumPlus (Premium Economy)
Y - Full Fare Coach
B - Full Fare Coach

M - Discount Coach
E - Discount Coach
U - Discount Coach
H - Discount Coach
Q - Discount Coach
V - Discount Coach
W - Deep Discount Coach
S - Deep Discount Coach
T - Deep Discount Coach
L - Deep Discount Coach
K - Deep Discount Coach
G - Deep Discount Coach
N - Basic Economy

Saver Award Inventory
IN - Elite (Plat/1K/GS) Saver Business or 2-cabin First Award
I - Non-Elite and Low Elite Saver Business or 2-cabin First Award
XN - Elite Saver Coach Award. Also available to Chase Explorer and Club cardholders as an undocumented benefit
X - Non-Elite Saver Coach Award

"Everyday" Award Inventory
JN - Elite/CC Everyday Business or 2-cabin First Award
ZN - Non-Elite Everyday Business or 2-cabin First Award (tracks to the Z bucket). Also used for buy-up upgrade offered at check-in.
ON - Everyday PremiumPlus (Premium Economy) Award
YN - Elite/CC Everyday Coach Award
HN - Non-Elite Everyday Coach Award (tracks to the H bucket)

Upgrade Inventory
PN - Y/B/M 1K Instant Upgrades (CPU eligible routes only); All GS upgrades Y->J (CPU, RPU, GPU, miles)
PZ - Upgrades to Polaris Business, United Business, or United First (excepting GS upgrades and 1K Instant Upgrades)
RN - Upgrades to Premium Plus

Points earning for all upgrades is based on the originally purchased fare. Also see below.

Upgrades Note that upgraded flights will post to your MileagePlus statement as Z(X) where the second letter (X) is the original booking class. The parenthetical letter defines the earning rate for the flight as points are earned based on the original booking class.