Apocrypha

(This issue arose from other reading but is relevant here.)

The Apocrypha are not esoteric documents but books that were included in the Septuagint, the Greek translation of the Hebrew Canon, and therefore also in the Catholic Canon but that were later excluded from the Hebrew Canon and therefore also from the Protestant Canon. I think that I have read about a further distinction between passages included in the Septuagint but not in the Catholic Canon but googling did not shed any light on this. Excluded books automatically gain a reputation for  hidden knowledge and/or heresy. In one useage, "apocryphal" means "false."

This concept can be transferred to future history series where there could be at least two kinds of "Apocrypha."

(i) Non-canonical works: a story might share background details with a future history series but in other ways diverge from the fictional history of that series. See Poul Anderson's "Symmetry."

(ii) Some installments are revised for later publication. Thus, the earlier versions could be collected as "Apocrypha." Poul Anderson's History of Technic Civilization has a few of these.