Going back to my res days on this one, so don't shoot me if I'm wrong. "DL" used to be the code that would be used if you were waitlisted for an upgrade, it cleared but then your travel agent didn't confirm it within a specific time frame so the airline would take it back and give it to the next person on the list. "DL" stood for "Deferred from List".

I'll try to log into Apollo and see if this is still the case. I will post an update if I find anything different.

-IFLYUA