That does gives us options. Each cabin could be unique in what features they have in addition to the standard two rooms and two doors with the spinning mirror/cabinet. As to Spock's cabin in "Amok Time" - there is room for a small toilet room next to the spinning mirror/cabinet. The camera never looks towards the "bedroom" door wall area. Perhaps it's a shared bathroom? since that door doesn't have a sign on the outside signifying it is Spock's cabin? I think in other scenes, both doors that have access to the cabin have a wall sign on it...?