The standard of brief is unclear and even whether all the participants attended a formal pre-sortie "brief" but what is for sure that SOPs in the military sense were non-existent.
The "standard of the brief" will be unclear if you weren't there.
There have been plenty of Balbos at Duxford since Legends took over from the Classic Fighter show. Obviously the "SOPs" in the past have worked - would be interested to find out how you think they were "non-existent" this time (without including this accident)...