Pathfinder Codices
Ecology
While various mineral deposits are always listed, one of the main values of having an environmental codex is its information on the flora and fauna of the region. They reveal information about extinct species, ancestors of current species, and species that currently exist. Usually, there are highly detailed anatomical sketches as well as a list of various materials one can harvest from these plants and animals that can be of use to someone living there.
Environmental codices can be a good source for a more effective poison found in the gland of a particular animal or from the juice of a particular berry. They can also reveal alchemical recipes and will list the most effective ways of taking down examples of fauna that are exceptionally difficult to kill.
The Maladies
They encountered Universal Melancholia as they traveled around the area currently known as The Black March, and even encountered Universal Mania, which at the time affected the western coast of Estoya. Much of the knowledge on the maladies known to those in the present comes from the codices and there are many more yet to be discovered.
Venom in the Glade sounds interesting, like a raid boss. Also, Pathfinder codices simultaneously seem like a great adventuring tool and a great plot hook for a more lore-minded adventurer. A wizard or bard could be on a quest to find and copy down as many pathfinder codices as they could before they are lost to time.
Yes indeed. Bards in particular. But its the Wardens who really benefit from them. They can craft the tools and make full use of the info they hunt. They are kinda my attempt at making rangers more interesting cause I always felt they get shafted a bit, but you hit it on the nose. That's exactly what I use em for.