Im looking at my Dads log book and Sqn ORBs and am curious why sometimes he writes that he was flying in (for example) aircraft W and other times he records a two letter and 3 serial number combination.

He was with 77 Sqn, so I know the KN letters and the single letter denote the aircraft, but did all planes at 77 Sqn have KN, but not all had a A-Z letter?

Were there always letters on the planes (seen in different images on the forward facing flat part of the landing gear and either side of the roundel)? Or were there sometimes just the Sqn prefix letter only?

I wonder why he sometimes just used the letter and other times used the aircraft serial number?