The Earth Book Of Stormgate

Poul Anderson's The Earth Book Of Stormgate (1978):

collects twelve previously published works, including one novel, The Man Who Counts (1958);

covers the histories of human-Ythrian relations and of the Polesotechnic League;

connects these histories by adding twelve introductions and one conclusion written as by an Ythrian;

derives the content of these new passages from the novel, The People Of The Wind (1973).

In the eleventh and twelfth Earth Book stories, "Wingless" (1973) and "Rescue on Avalon" (1973), as in The People Of The Wind, human beings and Ythrians have jointly colonized the planet Avalon.

People discloses that:

the Avalonian colony was founded by David Falkayn of the Polesotechnic League, a major player in the ninth and tenth Earth Book stories;
Ythrian social organizations are called "choths";
Avalonian choths include Stormgate;
Stormgate includes the family of Lythran and Blawsa;
choth officers are called Wyvans;
increasing numbers of human beings join choths;
these include Arinnian, whose human name is Christopher Holm;
the Terran Empire waged war on Avalon.

Thus, it makes sense when the opening introduction in the Earth Book informs us that:

Rennhi of the Stormgate Choth wrote The Sky Book Of Stormgate, a history of the choth's ancestors on Ythri, founders on Avalon and subsequent generations to her own time;
helped by her son, Hloch, she gathered material for a companion volume that would recount the human antecedents of the colonization  of Avalon;
Hloch served in space during the Terran War, traded on Imperial planets after the War, then returned to Avalon;
since Rennhi had died, the Wyvan Tariat, son of Lythran and Blawsa, asked Hloch to complete the Earth Book.

In his introduction to the eighth Earth Book story, Hloch informs us that Arinnian had prepared this version of the story for publication. Hloch and Arinnian collaborated on the ninth and tenth stories.

Eyath, daughter of Lythran and Blawsa, and Arinnian are friends and major characters in People whereas Tariat, son of Lythran and Blawsa, and Hloch are created for the new material in the Earth Book. By drawing on the background of The People Of The Wind, Anderson adds considerable depth to the stories collected in the Earth Book.