The rumpus room has only been seen in a few episodes. It is seen in "Three Men and a Comic Book", "Separate Vocations", and "Lady Bouvier's Lover". The above diagram is consistent with those episodes. In "Radio Bart" it is seen, but looks different (no built in cabinets. In "The Canine Mutiny" Laddie flushs a toilet where the rumpus room would have been. Since the room hadn't been seen in a long time, it is possible it could have been remodeled as a bathroom, but most likely it was another example of artistic license.