I think DL's been putting out some weird availability data lately. I wanted to book LHR-ATL-LHR but via MIA on the outbound (for miles) and MSP on the return (to visit friends on a long layover, but also for miles). EF was showing T9 for LHR-MIA-ATL, and ITA was showing it available in T as well. However, DL.dumb would only give me a ticket in K or Q or some combination.