In 1992 when BA EC North America was established, there was a Gold Reservation Assurance. It applied if there were no available seats in F, the Gold Member was guaranteed a seat in Club World even if there were no seats in J available for this flight.
I guess they've modified this benefit over the years. I'd have thought they'd guarantee a seat in CW rather than WT-
DL had a similar guarantee for Medallion members in full fare Y.