The other one (and the one I have) is old and mine is G-BOAC as well... no it wasn't worn on the ac, but many model types have that reg, even after Concorde wore it.
That's very nice! Hmm, I don't think I can smuggle that one past the border control back home. And the price is a bit too steep for a Christmas present. Oh well, one can dream.
Registrations on models commissioned by the airline are often chosen so that they don't represent a specific aircraft. In the event of an accident you don't want that particular aircraft in the window of every travel agent. I know that in the case of KLM they use a specific set of registrations for a type, e.g. PH-BF_ for 747-400s. Within this set they will not use the letters J, Q and X because they might cause confusion with other letters. On a model of a 747-400 that is commissioned by KLM you will see the registration PH-BFJ as this can never be a real aircraft and they will often paint the registration PH-BFX on the 747-400 simulator, I don't think they've found a use for the Q yet.