For the most part, The Past Through Tomorrow defines a core group of stories that are clearly within the Future History series. However, Heinlein scholars generally agree that some stories not included in the anthology belong to the Future History series, and that some that are included are only weakly linked to it.
James Gifford adds Time Enough for Love, which was published after The Past Through Tomorrow, and also "Let There Be Light", which was not included in The Past Through Tomorrow, possibly because the collection editor disliked it or because Heinlein himself considered it to be inferior. However, he considers Time Enough for Love to be a borderline case. He considers The Number of the Beast, The Cat Who Walks Through Walls, and To Sail Beyond the Sunset to be too weakly linked to the Future History to be included.
Bill Patterson includes To Sail Beyond the Sunset, on the theory that the discrepancies between it and the rest of the Future History are explained by assigning it to the same "bundle of related timelines" in the World as Myth multiverse. However, he lists a number of stories that he believes were never really intended to be part of Future History, even though they were included in The Past Through Tomorrow: "Life-Line" (which was written before Heinlein published the Future History chart; however, Lazarus Long does reference the protagonist of "Life-Line" and his device in "Time Enough for Love"), "The Menace from Earth", "—We Also Walk Dogs", and the stories originally published in the Saturday Evening Post ("Space Jockey", "It's Great to Be Back!", "The Green Hills of Earth", and "The Black Pits of Luna"). He agrees with Gifford that "Let There Be Light" should be included. The story "—And He Built a Crooked House—" was included only in the pre-war chart and never since.
The Heinlein juveniles do not hew closely to the Future History outline. Gifford states that "Although the twelve juvenile novels are not completely inconsistent with the Future History, neither do they form a thorough match with that series for adult readers. It is not often recognized that they are a reasonably consistent 'Future History' of their own... At least one major story specified in the Future History chart, the revolution on Venus, ended up being told in the framework of the juveniles as Between Planets." The novel Variable Star, written by Spider Robinson from Heinlein's detailed outline, incorporates some elements of both the Future History (such as references to Nehemiah Scudder) and the universe of the Heinlein juveniles (for example, torch ships and faster-than-light telepathic communication between twins). The adult short story "The Long Watch", included in Future History story collections, connects to Space Cadet through the character of (John) Ezra Dahlquist, the central character of the first, memorialized in the second.