Okey doke. I found the bit in the FFC I was thinking of. Its "Campaign Map Notes". In that section "Svenson, the Sinders, Monson, Nelson and Gaylord are all said to have (or had) "holdings" I suppose that makes them nobles but whether that qualifies for inclusion in your list could be a seperate question.

House Zov added to the Thonian Houses

-Havard

I just stumbled on this and thought it didn't sound familiar, so I checked the list here and didn't see it.
This quote is from page 224 of the DAB campaign sourcebook:

On the hilt of the dagger is a symbol showing a
large shield with a crossed handaxe; A DC 15 Knowledge
(nobility and royalty) check (reveals that this symbol
belongs to the noble Arthous family of Blackmoor.

Cool. How do you distinguish between lesser and greater houses? What about extinct houses?