The Tolkien book published posthumously in 1980 as an edited collection of unfinished Middle-earth stories is Unfinished Tales.
Christopher Tolkien edited and published Unfinished Tales of Númenor and Middle-earth in 1980. The volume gathers narratives and fragments from different periods of J.R.R. Tolkien’s writing, including material about Númenor, the First Age, and the Third Age.
Unlike a conventional novel, the book preserves incomplete drafts, variant versions, notes, and editorial explanations. Christopher Tolkien often identifies contradictions or changes between texts so readers can see how his father’s mythology developed over time.
The title is sometimes confused with The History of Middle-earth, Christopher Tolkien’s twelve-volume series published between 1983 and 1996. The Children of Húrin, published in 2007, is a later constructed narrative assembled from Tolkien’s writings, not the 1980 collection.