Mostly I'm curious whether there is any long tail prevention / a mercy rate that will guarantee a Legendary Book if you've opened enuogh boxes without receiving one, but really any element to how it works would be cool to know.
Are you more likely to get one when there's still many unacquired? Is it just a flat 1/x chance of being "a legendary book" then randomly one you don't have? Do they each have individual rarities?
Inquiring minds want to know!