HEDP, your logic is solid. I agree, it shouldn't be used twice IMHO (there is indeed a current middlewalloper version of this sqn numberplate).
Such contemporal existence only worked whilst the VGS remained a School and not a Sqn.
A quantity of former RAuxAF sqn boilerplates became adopted by the AAC following the 1957 cull (esp the Army Observation / Co-operation ones:
http://www.aaca.org.uk/aop.htm refers at least in part).
However, there is at least one current double-numbers precident I can think of (thinks....yes): 2 Sqn (GR4 variety) and 2 Sqn RAF Regt (rock variety). Or is their some get-out regarding roman numerals....no, don't believe so?
Odd that the AFB didn't notice the 663 clash, and deconflict. Arguably would only cause operational grief if both units were deployed to same theatre
.....
Meantime, I'm waiting for 633 to get activated (*must* be saved from the fates of the Aldershot Aviation Corporation
)- maybe it could be used as a hold for tramatised Offrs completing the new IOT: now *that* would be worth watching
wilf_san