This also ignores Tolkien retconning Arda in some editions to have always been a round Earth as detailed below and on the
Tolkien Gateway.
In his later life, Tolkien began to have misgivings about the "flat earth" cosmology of the First and Second Age, and made outlines of a plan to create an alternate "round world" version of his legendarium in which the world had always been round. He never completed this revision before his death, and so the "flat earth" stories were published in The Silmarillion. Tolkien's misgivings were primarily astronomical, having to do with the scientific absurdity of a sun that orbits the earth, a moon that glows from its own light, and stars that are points set in a firmament over the earth. How could our world emerge from such a beginning? The Round World version is one of the variants of J.R.R. Tolkien's Legendarium, published in the final volumes of The History of Middle-earth. In this version, the setting of his legendarium is more realistic and less mythological: the Earth was always round, and Arda was the name for the whole solar system instead of just the Earth.
In the Round World version the Sun and the Moon were not the fruit of the Two Trees, but actually preceded their creation. The significance of the Trees and the Silmarils was that they preserved the light of the Sun before it was tainted by Melkor when he ravished Arien.
Similarly, the stars were not created with the Awakening of the Elves, but the occulting clouds were removed to reveal them, and it wasn't Varda who kindled them, since her power was limited to Arda while the stars were set in Eä.
This version emerged in writings from 1958-1960, but it was never developed beyond the stage of drafting and Tolkien didn't continue the revisions. Thus the Flat World version was chosen by Christopher Tolkien for the published The Silmarillion. Tolkien had previously attempted to write a round world version of the Ainulindalë and the Fall of Númenor, but in both cases he returned to the flat-earth model. Beside this, references to the seas being first "bent" after the Fall of Númenor, to the "Sunless Years", and to the trolls of the Twilight, survived in Lord of the Rings.
The Round World version can be deemed by Tolkienists as the definite 'actual' story behind the text; the text of the Quenta Silmarillion then, can be seen as just the legends based on the 'reality', written by the ancient people of Middle-earth. In his last years, Tolkien didn't view his legendarium as having an Elvish origin, but a Mannish one, and thus the legends contained in it could be inaccurate. This can be seen as a commitment to retain the older legends in the context of Mannish transmission, without need to rewrite the tales, as Tolkien had attempted at first. I do admit that this is fairly speculative however and so I invite whatever conclusions we can draw on this.
