Dukes can use their influence to sway lords to their own Duchies. I've seen it happen.
It's a quite more realistic then to have Dukes just change regions back and forth from duchy A to B without Lords having a say. And it is a great opening from some game- and roleplay I guess.
The difficult part if the region is lordless, then there is no influence battle between Dukes.
Thank you for clarifying for me
