I have a flight to LIS booked near Christmas time. The outbound flight has been changed by the airline three times in three weeks. I'm curious to know if I've been moved off of some of those flights because the flights are cancelled or because the flights have sold out and passengers (such as me) have been moved to different flights for "load balancing". Either way, I assume that either a cancelled or sold out flight does not show up when doing a regular flight search either through a third party such as ITA or via the carriers website. So how best to determine if a flight has been cancelled or is simply sold out?