Trying to change to an earlier flight on 2/17, CUN-LAX, talked to PM line last week, they confirm me in Y (bought a J ticket) and said that someone was working on it...orig J segment still confirmed, plus the 2 Y segments (layover in ATL). Call PM line today as I'm getting close to the outbound and he says no flights avail on 2/17 in J/F except 9:15 am with 3.5 hr layover in ATL. I'm looking at dl.com and see that they will sell me about 10 different flights in J/F!! He says it must be a glitch and confirmed with supervisor that they won't oversell J...hmmm.

The funniest part is this shows up on My Trip:

You have-36m to change airports between ( LAX ) AND ( CUN )

With a schedule change, you may miss your connecting flight. Please review your scheduled itinerary.