End of March Update #2:
From Virgins Site:
S, T, A, U, X, R, F = Discount Economy
Y, N, B, M = Full Fare Economy (Flexi)
W = Premium Economy (Possibly Long Haul International PE translates into W for Domestic or Short Haul ... W seems to come from Business Class stock)
J = Business
AFF deduction, certainly open to review:
O = Discount J
H = Velocity rewards J
I = Economy (?? probably) reward or other non earning fare (Really unsure, some sort of Y fare that involves airline goodwill or last minute changes????)
D = Might be Government contract Economy, probably non earning - need more data
L = Economy (?? probably) reward or other non earning fare
P = Discount Economy Flex, most likely rewards or non earning related (or it would be in the discount economy listing from DJ)
C = Discount Y, codeshare bucket. Listed by DL and SQ as 50% earning Discount Y
E = Listed by DL and SQ as 50% earning Discount Y ... more data required .. if it were standard cash discount Y then it should be in DJ's list of discount Y. If it were straight rewards its unlikely to generate earn via partners.
Q = Points Upgrade or Comp (status) upgrade to J
R = Some sort of promotional class. Its listed in Virgins 'earning' classes (see top of post), but there is mounting anecdotal evidence that R class is used for Amex "free" flights. Also appears to be used for the Virgin "Flyer" and "High Flyer" 2 for 1 paid seats redemption when those seats are booked as economy.
T = Possible Amex / promotional class. Need some boarding passes to verify this.