A couple that you might need to follow..
THE LONDON GAZETTE, 7 MARCH, 1941 page 1375
Pilot Officer Wells Wintemute WELLSCOATES is granted the war substantive rank of Flight Lieutenant. wef 7th Jan. 1941.
(doesn't fit with your dates) but this might
page 5222 THE LONDON GAZETTE, 27 AUGUST, 1940
The undermentioned Pilot probation are confirmed appointments:— 3rd Apr. 1940.
Ronald Harrison Fitzgerald WELLS (31358)......"
and on the same page:-
The undermentioned Pilot Officers are promoted to the rank of Flying Officer:— 3rd July 1940, ........ Ronald Harrison Fitzgerald WELLS (31358) ........"
https://www.thegazette.co.uk/London/...upplement/5222
In April 1940, while flying Wellingtons (and while on temporary loan to RAF Coastal Command) 115 Squadron gained the distinction of making the RAF's first bombing raid of the war on a mainland target-the enemy-held Norwegian airfield of Stavanger Airport, Sola.
Perhaps that explains the rapid promotion?