The convention (to which I believe there was some big discussion on at the time in the 60/70's) was that the French were going to call it 'Concorde' and the British versions would be 'Concord'.
In the end the Brits ended up spelling theirs 'Concorde'.
Its often Americans that you hear referring to tehm as 'The Concord' Youll find that almost anyone that had anything to do with her did not use 'the' as a prefix.
I am sure someone else will be able to point us in the direction of a website that clarifies all this?