(...) Melkor, que foi o primeiro dos Ainur a ingressar em Arda!
Onde isso é dito mesmo? Já ouvi tanto isso que virou senso comum, mas não me lembro de onde isso está escrito nas obras...
Cara, você tem razão de perguntar isso! Tenho impressão que isso não aparece nas obras de forma explícita!
Achei nos Mitos Transformados II (Morgoth's Ring):
The Story, it seems, should follow such a line as this. The entry of the Valar into Ea at the beginning of Time. The choosing of the Kingdom of Arda as their chief abiding place (? by the highest and noblest of the Ainur,(5) to whom Iluvatar had intended to commit the care of the Eruhini). Manwe and his companions elude Melkor and begin the ordering of Arda, but Melkor seeks for them and at last finds Arda,(6) and contests the kingship with Manwe.
This period will, roughly, correspond to supposed primevalepochs before Earth became habitable. (...)
6. This is of course altogether different from the form of the legend in the Ainulindale' (p. 14, $23): 'But Melkor, too, was there from the first, and he meddled in all that was done'; while in the text C* (p. 40) Melkor entered Arda before the other Ainur.
O trecho do texto C* em questão é
So began their great labours [rejected immediately: in the beginning of Time and in the immeasurable ages forgotten] in wastes unmeasured and unexplored, and in ages uncounted and forgotten, until in the Deeps of Time and in the midst of the vast halls of the World there came to be that hour and that place
where was made the habitation of the Children of Iluvatar. And many of the Valar repaired thither from the uttermost parts of heaven. But the first of these was Melkor. And Melkor took the Earth, while it was yet young and full of fire, to be his own kingdom.
And they went thither, Manwe and Ulmo and Aule, and others of whom thou shalt yet hear, AElfwine, and behold! Melkor was before them; but he had little company, save a few
of those lesser spirits that had attuned their music to his; and he walked alone"and the Earth was in flames. The coming of the Valar was not indeed welcome to Melkor, for he desired not
friends but servants, and he said: This is my kingdom, which I have named unto myself.' But the Valar answered that this he could not lawfully do, for in making and governance they had all their part. And there was strife between the Valar and Melkor; and for a time Melkor departed and withdrew beyond the arrows of the Sun, and brooded on his desire.
Sobre o texto, é dito que
The fundamental difference between C* and C lies in this, that in C* the Sun is already present from the beginning of Arda (...)
Ainulindale C* was thus an experiment, conceived and composed, as it appears, before the writing of The Return of the King, and certainly before The Lord of the Rings was finished. It was set aside;
O texto do Myths II, ainda que pós-SdA, também deve ser encarado como algo experimental...
I have shown, as I believe, that when my father first began to revise and rewrite the existing narratives of the Elder Days, before The Lord of the Rings was completed, he wrote a version of the Ainulindale that introduced a radical transformation of the astronomical myth, but that for that time he stayed his hand.
But now, as will be seen in many of the essays and notes that follow, he had come to believe that such a vast upheaval was a necessity, that the cosmos of the old myth was no longer valid; and at the same time he was impelled to try to construct a more secure 'theoretical' or 'systematic' basis for elements in the legendarium that were not to be dislodged. With their questionings, their certainties giving way to doubt, their contradictory resolutions, these writings are to be read with a sense of intellectual and imaginative stress in the face of such a dismantling and reconstitution, believed to be an inescapable necessity, but never to be achieved.
Em resumo, há uma versão que Melkor chega antes de todos os ainur, outro versão que chega um tanto quanto depois, e outro versão que chega mais ou menos junto aos demais. Esta última versão é a que temos em O Silmarillion:
(...) mas Melkor também estava ali desde o início e interferia em tudo o que era feito (...)
Melkor chegando separado dos demais (antes ou depois) provém de textos ligados à cosmologia modernizada que Tolkien esboçou (heliocentrismo, terra redonda, etc.), e portanto textos experimentais e pouco "canônicos". Já o texto que "Melkor, too, was there from the first" parece ser o mais "canônico", e é justamente o texto que estamos habituados em O Silmarillion. Se não houver outros textos a respeito, essa parece ser a versão mais amadurecida sobre a questão.
Mas ainda parece difícil interpretar a fala de Tom Bombadil, afirmando que já existia "before the Dark Lord came from Outside". Christopher aponta, em The Return of the Shadow:
Tom Bombadil was 'there' during the Ages of the Stars, before Morgoth came back to Middle-earth after the destruction of the Trees; is it to this event that he referred in his words (retained in FR) 'He knew the dark under the stars when it was fearless - before the Dark Lord came from Outside'? It must be said that it seems unlikely that Bombadil would refer to Valinor across the Great Sea as 'Outside', especially since this was long ages 'before the seas were bent', when Numenor was drowned; it would seem much more natural to interpret the word as meaning 'the Outer Dark', 'the Void' beyond the Walls of the World. But in the mythology as it was when my father began The Lord of the Rings, Melkor entered 'the World' with the other Valar, and never left it until his final defeat. It was only with his return to The Silmarillion after The Lord of the Rings was completed that there entered the account found in the published work (pp. 35 - 7) of the First War, in which Melkor was defeated by Tulkas and driven into the Outer Dark, from which he returned in secret while the Valar were resting from their labours on the Isle of Almaren, and overthrew the Lamps, ending the Spring of Arda. It seems then that either Bombadil must in fact refer to Morgoth's return from Valinor to Middle-earth, in company with Ungoliant and bearing the Silmarils, or else that my father had already at this date developed a new conception of the earliest history of Melkor.
A impressão que eu tenho disso tudo é que Tolkien, no decorrer dos anos, mudou constantemente as entradas e saídas de Melkor de Arda, de forma que na época de O Senhor dos Anéis provavelmente não tinha uma imagem muito sólida sobre a questão. Melkor vir de Fora seria assim apenas um episódio do passado remoto que Tolkien ainda estabeleceria com maiores detalhes, e servia para mostrar a antiguidade de Tom Bombadil, mas não deve significar muito mais do que isso... A fala não nos permite afirmar, por exemplo, que Tom Bombadil estava aqui antes do que a totalidade dos ainur.
Pode-se interpretar, por exemplo, que Bombadil pudesse estar se referindo ao fim da Era das Lâmpadas, quando Melkor veio de fora de Arda (onde estava após ter sido expulso por Tulkas) e atacou Almaren. Anda que tais episódios não tivessem sido concebidos na época de O Senhor dos Anéis, parece coerente afirmar que o episódio da vinda de Melkor "de Fora", qualquer que seja ele, não estava solidificado, então só restaria mesmo uma interpretação em retrospecto...