Dora-9,
A small correction. When I was with UBAS from 1967 to 1969, I don't think the five UBAS Chipmunks were ever used for AEF flights. The Boss guarded his airframe hours very jealously!
On the other hand, I did occasionally fly other Chipmunks, but I'm not sure if they were 8 AEF's aircraft.
Incidentally, I've often wondered about the purpose of the individual letters. We never referred to them; we always used the serial numbers.