Tolkien's notes, published in History of Middle Earth, volume 11, The War of the Jewels,
from Grey Annals, written sometime in the 1950s“472: This is the Year of Lamentation ....”“... But even as the vanguard of Maidros came upon the Orcs, Morgoth lossed his last strength, and Angband was emptied. There came wolves, and wolfriders, and there came Balrogs a thousand, and there came worms and drakes, and Glaurung, Father of Dragons ...”
However, on the typescript of the corresponding passage in the Annals of Aman (written at roughly the same time), JRRT made the note:
“There should not be supposed more than say 3 or at most 7 [balrogs] ever existed.”
