<MT-era SPOILERS below>
Gah.
That one's spread out over a number of MT-era sources, as well as Survival Margin.
Basically, the process of Strephon's re-instatement of the Domains and their Archdukes had not yet reached the Marches when the Rebellion started. Seeing the need to have an Archduke, Duke Norris launched a super-secret-sacred mission to "recover" the Warrant that re-instated the Domain of Deneb and named him Archduke, and was, with this boost from the now-"dead" Emperor Strephon, able to steer the Domain through the local incarnations of the Rebellion.
Speculation about the validity of the Warrant was rampant throughout the MT period, since it was known that Dukes had a small supply of blank Warrants with which to work the Emperor's will. The question of this particular Warrant was not answered until Survival Margin, when one of Strephon's journal entries refers to Archduke Norris in both an amused and supportive fashion. Strephon hadn't sent the Warrant, but confirmed it when he (finally) heard about it via (I think) the visit of the Arrival Vengeance.
That what you were looking for?