The X's and O's in the doors are there to mark whether or not they can be entered, since I'm only using one-way doors for the sake of not having to worry too much about story flags. You're not the only one confused by them, though! There's gotta be a much better way to do that on my part, lol. Also, I just noticed I forgot to mark which key enters doors in the description.
Thanks for the playthrough! I don't have very much raw footage of this game, so it helps a lot.