Thanks for this video, I'm sure it will help people. What about the navmesh bug though? Can you test your new navmeshed area in game by maybe setting up some guards patrolling or just have a follower, go to that exterior cell, then run a few cells away and come back? Every time I do this in the exterior cell's navmeshes that I've changed, it bugs out the NPC pathing.
is a video of the bug in action, and from my testing it looks like the bug ALSO effects user-navmeshed exterior cells, not just interiors.