I can confirm that, on my flight a BA Premier on full R fare was left behind (forced to slum in subsonic F). BA does not overbook Concorde and doesn't bump anyone -- not even award seats. Might be the only flight in the world with such a policy. Just be sure to check in within the required times as there are always people on standby and BA will reclaim any seats missing the check-in deadline.
BA is not making any award seats available for the rest of the year. Any cancellations will be sold as R and not go back to the award pool. Almost every flight is leaving 100% full (this info is based on a chat with Special Services rep at JFK).