I should also point out that as someone who has reluctantly had to do a certain amount of database programming in my time, GLA makes no sense.
Databases should resolve, but this needs disambiguation - do you mean the city of Glasgow, or specifically Glasgow International Airport (as opposed to Prestwick). There are a few others - DUS, BRU, BFS etc, but
afaik, in these cases, the additional airport has come into play more recently.
I have often wondered why a new code wasn't introduced in these circumstances, but I suppose it is a simple question of airport politics - it was bad enough having the battle over Weeze being allowed to call itself 'Dusseldorf' - imagine the chaos if the 'original' Dusseldorf had to change to DSI, or whatever. But could Dusseldorf (both) have been DSF, etc?