MM8 had 9 contiguous zones, viz: Murmurwoods, Garrotte Gorge, Ravage Roaming, Alvar, Ravenshore, Regna, Ironsand, Shadowspire, and Dagger Wound. There were then the four elemental planes, and the Plane between Planes, but if you think about it, these are not really zones, they are a special type of dungeon. Consider, apart from LB or Town Portal, there is only one way in and one way out, which is via a specific door. You can't just go up to the land boundary and walk across as you can with the other zones (OK, except Regna, that has its own special rules necessary for the game). But even if you want to count these, that's only 14.

MM7 is broadly similar. There are 11 contiguous planes (12 if you include Emerald Isle, which I quibble over because you can't get back there), namely: Avlee, Tularean Forest, Deyja, Eeofol, Nighon, Harmondale, Erathia, Tatalia, Barrow Downs, Bracada Desert, and Evenmorn Islands. I would not argue too hard about including Celeste with those, because if you fall off one of the walkways, you end up in Bracada, but I'm a lot less certain about where to put The Pit. I'm tempted to class that as a special type of dungeon, like the Planes in MM8. But that's still only 14 if you include them all.