"A World Forever Lost"

Jack Finney's time travelers satisfy their nostalgia simply by relocating to a more innocent age but Poul Anderson's Time Patrolmen cannot do this:

"The Midwest of his boyhood, before he went off to war in 1942, was like a dream, a world forever lost...He had learned better than to return."
-Poul Anderson, The Shield Of Time (New York, 1991), p. 178.

Everard's knowledge of what happens after 1942, and indeed throughout history, prevents him from settling down happily in the 1930's Midwest. In any case, Time Patrollers, with their indefinitely extended lifespans, do not look forward to any retirement but instead remain active within the Patrol. Even if Everard, having lived in New York from the 1950's to the 1990's, were, like the Farnesses, to move to the 1930's, that entire decade would remain a very small part of his expected lifespan. He is bound to have a different perspective on any short period, however idyllic.

Revisiting Amsterdam after thirty four objective years - many more subjective - he wonders:

"Had that summer really been so golden...?"
-Poul Anderson, Time Patrol (New York, 2006), p. 479. 

Although he is reassured that "Amsterdam had not become the sewer that some people nowadays called it..." (ibid.), he cannot return to being that young Everard, "unburdened with too much knowledge..." (ibid.)

However, Deirdre Mac Morn's home period is "...a world forever lost..." in a more literal sense. Her timeline has been prevented from coming into existence so that she cannot possibly return to it.