  that's not true. There is a clear distinction, at the very least in the interviews. Parallel worlds are those that do not share Randland's history and/or flora/fauna. For example, the Ogier come from a parallel world and the Snakes and Foxes are each from a parallel world.  Mirror worlds represent Randland where something has gone to a major or minor extent differently - for example Hawkwing lost the war or instead of naming the infant Rand, Tam thought that Narg would be a good name. There are infinite number of mirror worlds but an unknown number of parallel worlds. Each parallel world can have their own mirror worlds.  