Of course they know where the stations are. But they don’t necessarily know the precise local of all the underground tunnels, exits, mechanical rooms, equipment, etc. The underground network is far more complex than what the consumer map hanging on the wall in the station shows.

During the Cold War, Russia managed to map huge parts of the world, sometimes with higher quality and more accurate measurements than the countries themselves! Especially noteworthy considering that some of those countries (like the UK) were trying their hardest to prevent those sort of maps being made in the first place, yet the Russians ended up with better maps of the UK than UK themselves.

Considering that that happened decades ago, I'm guessing their (and others) capability of doing those sort of things have only improved, not gotten worse. But that's just me guessing.