Other Planets

In Poul Anderson's The People Of The Wind, Tabitha Falkayn of Avalon hopes that, after the war, Philippe Rochefort will show her the Imperial planets that he has described. She mentions seven:

Terra;
Ansa;
Hopewell;
Cynthia;
Woden;
Diomedes;
Vixen.

I think that, of these, Hopewell is the only one that we know nothing about?

Terra is Earth;
the previous installment of the History introduced Ansa;
Cynthians and Wodenites are important characters in the series;
van Rijn is shipwrecked on Diomedes;
Flandry visits both Diomedes and Vixen;
Vixenites later colonize New Vixen.

The People Of The Wind is also an important link in our knowledge of the planet Merseia:

the Grand Survey finds Merseia just starting its scientific and industrial revolutions;
 
in "Day of Burning," the Polesotechnic League protects the by now interplanetary civilization of Merseia from the lethal radiation of a nearby supernova;

in The People Of The Wind, the interstellar Roidhunate of Merseia is small and remote but growing and aggressive;

in the Flandry period, the Roidhunate threatens the Terran Empire;

in the Long Night period, both Empire and Roidhunate have fallen.

Based on this information, a History of Merseia awaits an author.