I noticed that Delta is marketing DL 19 and DL 56 as "direct" LHR-LAX and LAX-LHR flights (with stops in DTW) on 9/2-9/30 only. The DL 19 and DL 56 flight numbers are currently used for "direct" service on LHR-MCO and FLL-LHR (both with stops in DTW), respectively, and they will return to those flights after 9/30.
Does anyone know why DL would play around with flight numbers like this before starting nonstop service on 10/26?
The corresponding DL 18 (MCO-LHR) and DL 57 (LHR-FLL) flight numbers will also be borrowed for other flights during the 9/2-9/30 period, but I haven't figured out what flights yet.