Future Histories, As Broad As They Are Long

Imaginary time has width as well as length. World War III both did and did not happen in the second half of the twentieth century - if we contemplate at least two parallel timelines.

Heinlein's early Juveniles do not fit into his Future History but strongly parallel it and even form an alternative future history. In his "Concerning Stories Never Written: Postscript" in the back of some editions of Revolt In 2100, Heinlein writes that he has addressed the themes of one of the unwritten story "...in two novels which were not bound by the Procustean Bed of a fictional chart..." and that it would be tedious to re-address them. It seems a shame to call the elaborate structure of a future history series a Procustean Bed or to associate it with tedium. More positively, we can say that the future extends sideways as well as forwards.

Much more obscurely, I deduce what must have happened in one branch of James Blish's Haertel mini-multiverse by reading what did happen in another, otherwise incompatible, branch.

Here, a passing reference to a "Crater" in Poul Anderson's Psychotechnic History is elucidated by referring to a longer explanatory passage in his non-series novel, Shield.