[R.R.J Tolkien]

Originally Posted by Eldorion

The idea of Maiar did not yet exist at the time Tolkien wrote the encounter between Gandalf and Durin's Bane. The main text of LOTR was finished by 1949 (and the Moria material was first written much earlier), but the Maiar did not enter enter the picture until the 1950s during the reworking of the Annals of Valinor into the Annals of Aman. Morgoth's Ring discusses this in the chapter of that name.

The idea that Tolkien's cosmology -- or really anything else about the First Age -- was ever "finished" is a misconception and will impede any attempt to make sense of his writing. He obviously continued to tinker with the later Ages as well, but he tended to consider himself bound by published material except in the course of preparing new editions.

Nice to see you on this forum as well my wise friend. I am not one to question you so it seems I must accept maiar was not fully developed yet. However the strength of the balrogs and at least some of the history of them seemed clearly finished in the letters of tolkien at this point. He had even previously tried to publish what he saw as a consistent [few touch ups] sillmarillion with the LOTR. I would also say while he may have never totally finished the sillmarillion due to lack of energy in old age, he thought it close to finished and tells of its history many times in its letters that matches the published sillmarillion we have today.