I don't know the details on Continental (since they don't fly their own metal to CHA, just codeshare on NW commuters), but as a general rule, A and F are used to designate first class (one is award seats and one revenue seats); C and J designate business in the same way. (Which letter means what varies.) Other letters are normally coach, with Y being the full coach walkup fare, B usually a little more restricted (eg 3-day advance), and the rest follow randomly.