If you try to import a game (at lichess.org/paste) that's already been imported, you get the result of the previous import; the game isn't duplicated.
However, if you import a game that was broadcast, you get a new import (and a new server analysis that differs slightly from the existing server analysis). For instance, the third game between Carlsen and Nakamura on the first day of the finals in the New in Chess Classic tournament was broadcast here: lichess.org/broadcast/new-in-chess-classic--finals/finals-day-1/BueO56UJ and imported here: lichess.org/60l8pzZM.
It seems it would make sense to avoid the duplication just as in the case of a multiple import.
However, if you import a game that was broadcast, you get a new import (and a new server analysis that differs slightly from the existing server analysis). For instance, the third game between Carlsen and Nakamura on the first day of the finals in the New in Chess Classic tournament was broadcast here: lichess.org/broadcast/new-in-chess-classic--finals/finals-day-1/BueO56UJ and imported here: lichess.org/60l8pzZM.
It seems it would make sense to avoid the duplication just as in the case of a multiple import.