Duplicate maps

Why are there duplicate maps in the game? For instance: The Ancient Cave (191 and 192) are two instances of the same map, one is for the majority of the map filled out with chests and exits, then the other is just the last room. Both maps have the full map, but they split up the exits and chests so that there are two instances of the map.

Does anyone know why they do this? I'd like to use some of these duplicates to make new maps, but if I'm going to totally screw up my game in the process, I obviously don't want to do that.