[William Cloud Hicklin]

Well, Tolkien himself couldn't make up his mind about it; this can be seen in the 'round-world' Downfall of Anadune and related papers ca 1945-6 which were later explicitly rejected in the 'flat-world' Akallabeth. There are elements of the Appendices dating from around 1949 which greatly suggest the round-world story, and others which entered circa 1954-55 which are flat-world.

I don't think Tolkien felt up to the massive work of recasting the fundamental cosmology, in effect jacking up the house and replacing its foundation; while the idea of a distorted Mannish version has appeal, it also has problems for whatever fictional theory of transmission Tolkien might have decided on. Bilbo's "Translations From the Elvish?" Bilbo had direct sources of information in Elrond, Glorfindel and sometimes Gandalf to set him straight. Akallabeth written by Elendil? Elendil personally lived through it and would have known the form of the Old World. Surviving Gondorian manuscripts? Don't fit especially well as a co-transmission with the memoirs of two Shire-hobbits.

I'm not saying the problem was intractable, but Tolkien certainly never worked it out, and CT wisely kept silent.

In any event, whatever Tolkien's intentions for transforming the cosmological myth, his ideas were only notes and jottings that never received narrative form, and CT would not have been justified, I think, in replacing the completed QS and AAm texts with material of his own devising "based on" notes and jottings.