In chemistry a lot of the foundational synthesis and work is as old as the 60s and 70s; people build on it, but in some cases those early papers said pretty much all there is to be said on a topic, so there’s no reason to republish on it.

I’ve had to cite papers as old as the late 30s before, because no one has ever found anything to fix or correct about their work! Pretty impressive if you ask me, given how few tools they had.