Technically this is not correct, as e.g. a fully paralyzed and mute person can’t employ their knowledge, yet they still possess it.

You'd have to be past Hawkins levels of paralysis to not be able to employ that knowledge to come up with new physical theories. Now that was a nickpick.

You can still pick the book up and extract the knowledge.

That would be employing my knowledge of maths, of my general education, not of the QM knowledge represented in the book: I cannot employ the knowledge in the book to pick up the knowledge in the book because I haven't picked it up yet. Causality and everything, it's a thing.