Early Preview

The first three items in Poul Anderson's The Technic Civilization Saga, Volume I, The Van Rijn Method, are:

"The Saturn Game," set in the mid-twenty first century;
Hloch's Introduction to "Wings of Victory," fictitiously written after the events of The People Of The Wind which is set in the twenty ninth century;
"Wings of Victory," set in the mid-twenty second century.

(I refer to dates as given in Sandra Miesel's Chronology of Technic Civilization. For a discussion and proposed revision of the Chronology, see here.)

Thus, the consecutive reader receives an unexpectedly early preview of a considerably later period. What an appropriate way to introduce a future history series. When the remaining Technic History stories were to be collected, Anderson wrote Hloch's Introductions to them and they were published as The Earth Of Stormgate which exists in the History as well as in reality. Hloch refers to the Terran War, recent to him but far in the future for the characters in "Wings of Victory," in the same way as novels written in the second half of the twentieth century refer to "the War," meaning the Second World War. Patient readers will eventually read about the Terran War in The People Of The Wind but, before that, the Solar Commonwealth and the Polesotechnic League must come and go and the Terran Empire be founded.

When the entire Technic History was finally collected in seven volumes as the Saga, compiled by Hank Davis, the Earth Book stories had to be separated to go into their proper chronological places but, fortunately, Hlch's Introductions were retained. Thus, an unexpected consequence is this early preview of a later period.