Billy Drake was promoted substantive Wg Cdr on 1 Jan 53 but on retirement on 1 Jul 63, he retained the rank of Gp Capt.
This usually results from one of two things. During the war he held the rank of Gp Capt acting or war substantive or he had been an acting Gp Capt at the time of his retirement and was authorised to retain same as a courtesy.
Old Duffer