Then there must have been an absolute mountain of staffwork, risk assessments, poring over bow tie charts and great ignoring of the major risk to life on everyone's risk register -mid air collision (MAC) - before someone very high up was forced into accepting the responsibility for this.
The glory that is MAA...............
I would suggest that the risk of mid-air collision in a well briefed close formation sortie is minimal. The fact that they were mixed types flown by civilian and military crews is irrelevant so long as the guys were competent/current etc. I've no doubt that somebody senior was more than content to initial the auth sheet.