Gathering The Haertel Scholium

(i) We begin with six novels (although two are short):

Welcome To Mars
The Star Dwellers
Mission To The Heart Stars
A Case Of Conscience
The Quincunx Of Time
Midsummer Century

- and with six shorter works spread across two collections:

in Galactic Cluster
"Common Time"
"Nor Iron Bars"
"This Earth of Hours"

in Anywhen
"No Jokes on Mars"
"A Dusk of Idols"
"A Style in Treason"

(ii) A Case Of Conscience belongs with the After Such Knowledge Trilogy.

(iii) Of the remaining works, six form two pairs:

Welcome To Mars and the Galactic Cluster trilogy are linked by the character of Adolph Haertel;

The Star Dwellers and Mission To The Heart Stars are linked by Jack Loftus and his colleagues;

Midsummer Century refers to Thor Wald and the Dirac beep which were introduced in The Quincunx Of Time.

(iv) Finally:

"No Jokes on Mars" connects with Welcome To Mars;
"A Dusk of Idols" connects with The Star Dwellers;
The Quincunx Of Time refers to both "A Style in Treason" and Midsummer Century.

Thus, the Haertel Scholium could be six volumes or one omnibus volume with A Case Of Conscience collected separately as part of After Such Knowledge.

(The Quincunx Of Time is a novelization of "Beep," which is also in Galactic Cluster.)