Emergent Structural Similarities

Robert Heinlein's Future History
Five volumes.
However, Vol V is a short appendix about later events elsewhere.
The future social and political history of mankind from 1951 to about 2210 is complete in Vols I-IV.
Vols I and II are collections.
There are two novels.
However, there are also two short stories set between the two novels.
Therefore, Vol III is a collection of one novel and the two stories.

By Poul Anderson's "Polesotechnic League future history," I mean that part of Anderson's Technic History that covers the League and subsequent centuries but that stops short of Dominic Flandry's lifetime. This League history corresponds to Volumes I-III of Baen Books' seven-volume The Technic Civilization Saga, compiled by Hank Davis.

Poul Anderson's Polesotechnic League Future History, Original Version
Six volumes.
The Polesotechnic League Tetralogy and two Avalonian volumes.
The Tetralogy is two collections followed by two novels.
The Avalonian volumes are one novel and one collection of eleven stories and one novel.
Two stories in the Avalonian collection are set between the two Polesotechnic League novels.

"Lodestar" is explicitly set between Satan's World and Mirkheim:

"This happened shortly after the Satan episode..."
-Poul Anderson, "Lodestar" IN Anderson, The Earth Book Of Stormgate (New York, 1979), pp. 368-408 AT p. 375.

"Also in the records left on Hermes was information about an episode which had long been concealed: how Nicholas van Rijn came to the world which today we know as Mirkheim."
-op. cit., p. 368.

Satan's World is about an external threat to the League. "A Little Knowledge" (the other intermediate story), "Lodestar" and Mirkheim are about internal problems of the League. David Falkayn averts the threat and addresses the problems. In "Lodestar," he alleviates inequalities and in "Wingless" (the next story in the Earth Book), he reestablishes liberty outside human space.