Hmmm I don't actually think it's unfair. Like games can reward players who know more, from playing the game more or experimenting, for example game might reward player for knowing a solution to a puzzle from previous playthrough or give a player bonus items for getting out of bounds. It's not unfair per say then. And your game already has this in a place sort of, players who take time exploring or have played the game more than once will likely memorize the bookshelf placement. Some might even set up the early game by scanning the all of the given books first and then placing them in front of the book shelfs without putting them in, in order to get through multiple books in a quick session (I did that lol, reason why I found out about the crouch actually). So forgive the long text here, I think it's fairly reasonable to discover it only at late-game, or not at all :D