I think I see where the confusion is. The Hero, Monster, & Trickster are intended to be the three Story models, & each model has two abilities specific to them (Tough is an ability, for example).
Basically, the intention was for the Librarians to have a Hero, a Monster, & a Trickster, with their own set abilities already so there's no need to choose anything. What's listed is what the Librarians get.
I'll definitely keep this in mind next time I write a mission. Thanks!