Not sure if this really justifies its own thread but I've just cancelled 2 return J redemption seats LHR-SEA-LHR on August 16th/30th, and they've re-appeared for booking. This was my first booking under the new guaranteed availability system, booked in January, if that's a useful data point to BA's approach (both flights have I availability).

Given the West Coast is hard to redeem to, especially in summer, I thought someone might like to know about it. There don't seem to be any other seat pairs to SEA until November.