Davef68
The FG is just to make life easier for everybody, it wouldn't necessarily stay on the aircraft.
As an example, at Brüggen in the eighties the aircraft had the following fleet codes:
14 Sqn: AA, AB, AC etc.
17 Sqn: BA, BB, BC etc.
20 Sqn: CA, CB, CC etc.
31 Sqn: DA, DB, DC etc.