In this save I have Morian The Ruin Of Summer  about to enter my territory but I Can't find Plaguelands Swamp wildlands.

Looking at the map with the reveal cheat it looks like it was in the area of my Gwenneth's army, several AI outposts, and the  AI towns of Mirthranda and Timbraikat.

There is a non-existing river system shown here.

Given that Morian still exists and that there three strong groups of creatures in the area, two right next to Mirthranda, I dont believe that the Swamplands have been cleared by the AI and yet the AI appears to have settled them.

Nakisisa