Two Boxed Sets?

Three Future Histories
Cities In Flight
The Seedling Stars
The Haertel History

Three Trilogies
Heart Stars
Quincunx
After Such Knowledge

You might have to read or reread previous posts to see what I am getting at here.

The future histories culminate respectively in:

Volume IV, The Triumph Of Time;
Book Four, "Watershed";
"This Earth of Hours."

Citiess In Flight, Volume III, is Earthman, Come Home, a title that could be applicable in different ways to both "Watershed" and "This Earth of Hours."