Originally Posted by
jimrpa
Delta's "discounted" business fares are D and I. D is slightly discounted, I is significantly discounted, with significant restrictions. Both fares are eligible for all the regular COS bonuses, etc. Other than reward fares (O), Delta does not have any published purchasable business class fares that do not qualify for the business class bonuses.
Many years ago, Delta was experimenting with a system whereby the lowest COACH fares (L, U, and T) would only qualify for 1/2 the MQMs (and mileage) of a flight. Hence, the mnemonic ".5LUT" fares came into being.

Isn't "A" a discounted FC fare as well?
"N" is the fare code for a milage award seat.
Saw a "V" fare once... I was sitting next to Kelly Osborne... got her autograph for my daughter's scapbook. She kindly signed the back of her BP. Of course I studied it and noticed no SM# (guess she doesn't care or need to keep up with her miles) and the fare code was "V", for "VIP"?