It may have been due to the upheaval of the move to Cranfield,a change towards `tutorials` and syndicates,arrival of QFIs for conversions,a large Course(33),and a lot of aircraft(33) as well. There were also a lot of `dark blue` aircraft in the offing ,such as Wyvern,Attacker,Spearfish,Vampire , which may have required RN pilots of senior experience ,as most on the Course were short toured,(not suggesting that there was anything like the recent RAF v RN power struggles!). From 5 Cse on it also looks that there were also a lot more Foreign students as well.
I`m sure there may still be somebody out there who would have the answer,or it may still be in the ETPS archives.