Last and First Men by Olaf Stapledon is a history of the next two hundred million years. One of the Last Men on Neptune induces Stapledon in the twentieth century to write a history of the future. Stapledon thinks he is writing fiction and, in fact, the central nervous system of a First Man distorts most of the Neptunian's thoughts.
The Future History by Robert Heinlein is stories and novels set in the period from 1952 to the twenty second century. Let us suppose as a fictional premise that the Future History occurs in a parallel timeline mentally accessed by Heinlein while writing and that there was distortion. We may then deduce that Rhysling, the Blind Singer of the Spaceways, must have written better poetry than the verses attributed to him by Heinlein. Perhaps poetry is particularly difficult to transmit between universes.
Heinlein had frog-like Venerians who found eating obscene and had to do it alone. Stapledon had had frog-like Venerians and also Neptunians. Some of the latter found eating obscene and had to do it alone. Some of Heinlein's characters travel physically to the past or future. Stapledon's characters can visit only the past and then only by occupying the central nervous systems of earlier beings.
Heinlein was the first American future historian whereas Stapledon followed Wells in British sf. Both followed Wells in writing about time travel, space travel and alien invasion.