Quick edit for tonight - I've switched to "Mn" for the Mnemosyne Principality allegiance code in Far Frontiers - Dale's manuscript predates two letter codes, so I decided to follow BeRKA's lead.
While I was there, I made sure the borders lined up. I waffled on this - Dale's manuscript actually has closed borders for the Principality, unlike the Trelyn Domain which clearly extended outside of the sector. In the end, I decided to go with merged borders with Foreven.
If I ever had to waffle back the other way, I'd explain that the Principality is divided into two administrative provinces with a division along the sector boundaries. Or something.
(Some day I'll have to tackle the Julian Protectorate. That's going to be a lot less fun.)