Three Major SF Series

Each of these three major sf series could appropriately be republished in two omnibus volumes.

Robert Heinlein's Future History
Volume I should end with "Logic of Empire" - indentured servitude on Venus and a Prophet rising on Earth. The message is that things must get worse before they can get better and, sure enough, Vol I begins with a theocracy in the US and an interregnum of interplanetary travel. FTL interstellar travel does not begin until considerably later in Vol II.

Poul Anderson's Psychotechnic History
Vol I should end with "Brake" - escalating social chaos and irreconcilable ideological conflicts on Earth. Again, the message is that things can only get bitter. However, Vol II leaps past the Second Dark Ages and directly into a period of FTL interstellar travel.

Anderson's Time Patrol Series
Vol II should contain only The Shield Of Time and "Death And The Knight." Vol I should end with "The Year of the Ransom" and "Ivory, And Apes, And Peacocks," in that order. Wanda Tamberly first appears in "...Ransom." Everard fights Exaltationists in both "...Ransom" and "...Peacocks." Litlle do we know that:

The Shield Of Time will begin with Everard just returned home from his assignment in "...Peacocks";
he will round up the remaining Exaltationists;
Wanda will return;
Everard and Wanda will experience two divergent timelines, meet a Danellian, learn the real meaning of the Patrol and start a relationship that will continue in "Death And The Knight."

An extremely comprehensive series.