The Survival Of Sanity

In Poul Anderson's Technic History, we trace how certain planets, like Atheia and Kraken, survive from the Terran Empire through the Long Night into the Allied Planets period and Vixen, which was part of the Empire, has a colony, New Vixen, in the even later Commonalty period.

In Anderson's Psychotechnic History, the Psychotechnic Institute is outlawed after the Humanist Revolt of 2170, yet psychotechnicians serve the much later Galactic civilization so how did the science of psychotechnics survive? Well, over that long a period of time, it could have been rediscovered. It might not even have been called "psychotechnics" in both periods. Valti and his contemporaries speak the same twentieth century languages as we do but the text from the Galactic period has had to be translated into American English for our benefit!

However, there are some clues as to the survival of psychotechnics (see here):

the Planetary Engineers preserve psychotechnic training;

their Order is led by a Coordinator who may be linked to the Galactic Coordinators of the period of interstellar exploration and to the later Stellar Union Coordination Service, which uses computers called "Integrators," and whose field agents are called Coordinators;

some "Cordies" join the Nomads who preserve knowledge after the Stellar Union period;

the Galactic civilization applies psychotechnics and Integrators.

That explains why the Forewords and interstitial passages written from the standpoint of the Galactic civilization reflect a period when psychodynamics is taken for granted.