The History of Middle-earth
The Tolkien scholar Corey Olsen notes that Christopher Tolkien chose to present the incomplete tales as they were, adding a commentary to help readers grasp how they fitted in to his father's Middle-earth legendarium. Olson comments that the book's commercial success demonstrated the existence of a market for more of Tolkien's writings, opening up a route to publication of the 12-volume "The History of Middle-earth".