The former was re-coded in 1963 and the latter in 1980

When Washington National was renamed for Reagan in 1998 it still retained its DCA code.

I guess it’s just to complicated to re-code an airport these days given how widespread and interconnected the codes have been embedded into various systems and the chances of something going wrong are just too great with incorrect bookings and so on.

Airports themselves might get a new name but their 3 letter code is now basically for ever..