I understand that it may not show up if there are no award seats available or in paid searches if its sold out. That is when I went to the timetable to check the flight and it didn't show up. About 2-3 hours after I first saw it missing it returned. Yes, I'm aware that it can be changed for $75 + change in fare (or in this case miles) but award seats are hard to come by at the saver level so I've been checking frequently to see if any open up. However sometimes depending on the circumstances, schedule changes can work in your favor allowing you to change a ticket free if you can convience the agent that the changes made are inconvenient or somehow else unacceptable.