Not sure whether his has been said, but I often put together 2 separate DL tickets when paying out of pocket for BC, as in domestic A to B (F or MC) where B is a busy gateway overseas with cheaper BC tickets due to competition, and then a separate BC ticket from B to C. I have never had problems checking luggage all the way through starting in 'A' or returning from 'C' (even from France!!) - and further more, the few times the return flight has been late enough to misconnect on my ticket from 'B' to 'A' I have always gotten a curtesy rebooking if both flights are Delta coded, though once or twice had the DL agent tell me that they 'didn't have to do that'. When going from 'A' to 'B', I always have a contingency plan in case the first flight is delayed or canceled as in taking an earlier flight with a next flight making it in time or being ready to gate purchase a ticket to 'B' on another airline (had to do that once on UA) - Works for me, but you have to be prepared for IOPs and be ready to roll with it.