Mutley,
My point was that in database terms, BFS needs disambiguation. In consumer terms, BFS is confusing. LON, PAR, MIL etc are generic - ie they apply to the city as a whole. They don't represent individual airports. BFS can mean Belfast (either) or Belfast (Int). That is satisfactory in an industry that relies on precision.
In most cases, the 'confusion' isn't that much of a problem - eg GLA would easily be understood as meaning Glasgow Airport, not Prestwick as Prestwick is smaller and much further away. But in the case of BFS and perhaps also GOT, the smaller airport is much closer to the city centre.