How about a peer review system. Say we make a google doc and have people who read the book, rate it on its content on that doc. Perhaps if it has more that x number of favorable comments then the book can be deemed vetted for knowledge.The ban on learning things from books is unlikely to be lifted as long as books exist whose entire contents is
"*The bearer of this book is considered to know the dwarven language.*" For a particular example.
I've got the largest private collection of books on the server, and the number that I'd say count as solid knowledge references... I can't think of any off the top of my head.
Lifting this constraint requires staff to vet books for knowledge across all authors and requires them adjudicate content. Suggestions that drastically increase the burden of work in the Lore/Moderation department are.. unlikely to meet success.
You'd need plugin-based support and a skills system of some sort for tracking too, because otherwise I can say "My character got X from book Y" and without a plugin it's even more work.
It could be the writers responsiblity to have it read by others and vetted. If we all chip in and ooc vet some of them, then bam done.
Bear in mind we may not have to do this for hundreds of books. We would only have to vet the ones that try to teach the player about something, not the history ones or the journals as those are subjective.