So as I continue to do planning for my next novel, I've come to realize I will probably need to build a glossary for both point of view characters. The magic system involves synesthesia, and both characters are magic-users. Their forms of synesthesia, however, are very different, which means that given the same scene, both would perceive it with unique aspects. That said, synesthesia is consistent within the individual, which means that to save my sanity, I have to keep track of the links I create without constantly having to search back through the manuscript. I also have a couple other magic using characters in the storyline, which may mean making notes on how they "see" (or otherwise) things.
I am planning to have a few conversations revolving around the narrators seeing another character through different lenses. I also might make a point of describing a significant landmark or two, but I haven't decided yet. Certainly I want to make sure that I do pay attention to the synesthesia and not just brush it off as an intermittent special effect, and I think setting up a glossary will help keep me focused.