I never plunged far into 'Lorenverse'. GT was an interesting take on the Traveller Universe for me. I do find the CT verse the strongest pull for IMTU.
The whole assassination, virus etc...never appealed to me.
I usually run in the CT 1105-1115 era, but using MT rules. I have, however, enjoyed the mechanical consolidations made possible by MT for use in the 5FW. PC's as the cadre of a Marine Regiment, etc...
That said, MT didn't give any new labelled duchies.
Which means a fallback to Aramis is a county subsector, nominally answering to the duke at, Regina and Mora dukal subsectors, Jewell being subordinated to Regina (perhas a county, perhaps direct members of the "regina subsector"...
Aramis is a county and answers to the Duke at Rhylanor...
So I can find only 3 known explicit dukes (Mora, Rhylanor, Regina) in the Marches by non-GT sources. We have one county implied, and answering to one of the dukes. We have two districts which are not under a noble at all (Five Sisters aka 267, and 268).