Where Is The Black Nebula?

In Poul Anderson's History of Technic Civilization, the author writes the introductions that are fictitiously written by:

Francis L Minamoto;
Hloch of the Stormgate Choth;
Vance Hall;
Noah Arkwright;
Le Matelot;
Urwain the Wide-Faring;
Donvar Ayeghen, President of the Galactic Archaeological Society.

(Have I missed any?)

In Baen Books' The Technic Civilization Saga, the first complete uniform edition of the Technic History, editor/compiler Hank Davis writes the one new introduction that is fictitiously written by Michael Karageorge, a contemporary of Donvar Ayeghen.

Karageorge writes that the few clues as to the location of the Black Nebula use names of stars that fell into disuse centuries previously. The story, "Sargasso of Lost Starships," informs us that the nebula is a spherical dust cloud a light year in diameter ten parsecs beyond Ansa towards Sagittari. This sounds clear enough. And Ansa, a colony planet, is still inhabited a few centuries later in Dominic Flandry's time.

However, "Ansa" is the Anglic name of a planet. We are not told the name of its star. Further, Ayeghen and Karageorge live a very long time after Flandry. Ayeghen refers to the Empire founded by Manuel Argos as "...the First Empire..." (Rise Of The Terran Empire, p.325). We know of no subsequent Empires although we do know that human beings spread further during the four or more millennia after Flandry. Daven Laure, a Ranger of the service organization called the Commonalty, reflects that:

humanity has thinly occupied parts of two or three spiral arms;
the Commonalty operates in only one civilization, where it has members on ten million planets;
other branches of humanity have distinctive ways;
there are rumors of even stranger ways.

Thus, although the Commonalty has no wars or imperialism, there could well be empires elsewhere and Ayeghen's phraseology confirms this. Sol and Old Earth are fifty light years from Ansa but two spiral arms away from Daven Laure so Karageorge, wherever/whenever he is, is probably right when he says that the Black Nebula will be difficult to locate, especially if the name of their organization, the Galactic Archaeological Society, means that Ayeghen and Karageorge belong to a civilization that is not confined to part of one spiral arm but spans the galaxy.