I doubt there would be a schedule change this late in the game. Something appears to have happened and I would get NCL's air desk to call Delta to check this. They are not likely on Delta's direct computer system so what their airline system shows and Delta could be different. Also, it is possible to pull a ticket number and not have a reservation. I would also call Delta and see what they can see in history. Even if the reservation got somehow cancelled, the reservation shell with all the pertinent information would still show in Delta's system for a predetermined number of days after the original flights.