If YYZ can refer to Toronto (there is, by the way, logic behind this, which I have explained previously) then anything can be used !
It is surprising however that cities where major political changes lead to name changes (Saigon, Leningrad, etc) still refer to the "old days" a generation or more afterwards. It's not as if changes are impossible, but they just seem to not take place very often. It does seem that IDL became JFK almost at the same point as the airport name changed. Fortunately this has not spread to the current US fashion of politicians renaming airports after themselves, eg Atlanta, where they seem to like to rename it and re-rename it after various Mayors in succession.