There's already a tradition of the people keeping secrets even internally for various reasons of concern or danger.
See: the Carrion Eaters.they carry around surgical tools and little dolls with wound markings to serve as shorthand for what treatments to apply when they are in a hurry and need to consult their notes quickly. People find these intensely creepy and there are all sorts of stories about what they actually do, and the Carrion Eaters sometimes encourage them.