While the second to last letter in fare basis codes tells you these are all First Class fares, it doesn't tell you the actual booking class if that is what you want to know. KA0VA0FJ fares book into 'I' booking class. UAUQA0FB fares book into 'Z' booking class. And BA0PA0FL fares book into 'C' booking class. There is a dual-inventory check made when selling these fares. There must both be inventory in the coach bucket indicated by the first letter of the fare basis code, as well as inventory in the booking class bucket for the fare. Basic Economy and Comfort+ fares work the same way. So when a particular coach bucket zeros out, the BE, C+, and FC fares automatically also increment to higher fares along with the main cabin coach fares. So if a flight has inventory in 'Z' FC bucket, but no inventory in the coach 'U' bucket, you won't be able to buy the UAUQA0FB fare on it. At any rate, while DL uses the term 'upsell' fares and the fare basis codes start with coach class letters, these are all considered true FC fares and not coach fares as indicated by second to last letter in fare basis code.