Something as flimsy and malleable as lore should never, ever be used as a reason for not adding content. That's part of the beauty of lore; you can just come up with pretty much any ol' BS and it becomes part of the lore. It wouldn't be questioned. It just is.
This. Or the previously silent empire decided to open its doors to the outside world for whatever reason (events of ToAU, etc.). Or Naja partnering with A.M.A.N. to aid in soldier training. The empress already decided to mass recruit mercenaries from foreign lands, so it's not even a stretch. That's existing lore.
Where would this lore even go, anyway? Not like there was some cutscene necessary to use the books before. We just walked up to them and started on pages. Don't really need a reason; here are the books, start killing.
Hell, look at Trust magic. It just popped up outta the blue and all the characters are perfectly fine with it. We can run around with a magic sex sla- er, clone of the empress and other important figures to do our bidding no problem, but story-less exp books are an issue?