The Air Force List collated gazette dates of gradation for seniority in rank.
Wartime ones are on line at the National Library of Scotland.
Looking at a snapshot of July 1943 (which usually is correct for promotions to the two months before)
List him as F/Lt with seniority in rank from 28th Feb 1942.
http://digital.nls.uk/british-milita...chive/96295434
So as far as Authority was concerned he was still a F/Lt as of May 1943.
Flick through the later months to see when his substansive promotion to S/Ldr was listed in AFL and it's seniority date.
Ross
Ross