Another note...… I don't know if Delta does this but at least one carrier used to sell "discount" tickets to these tour companies with the understanding that basically they were buying "a flight home on day X". The airline could then move them at will. (It apparently was highly profitable because when I booked some kids on a tour and said "no thanks to airfare" all kinds of "hysteria" ensued from the tour company with bizarre made up circumstances that could ruin the entire trip LOL!)