Good report and research, thanks.
Hm.. nobles. I think they were initially named differently?
I think they were called body guards, but when I looked I could only find so much..
http://web.archive.org/web/200111230...how&BID=161844
Pending update:
-nobles and isabella cellus will be on 6 min spawn timers
-npcs that were 22 min spawns in high hold keep will now be 18 min spawns.