Well, I said the matter of Balrog numbers, and let me complicate that a bit more then
Yes Tolkien clearly made one marginal note in the later 1950s [or sometime later, as it's hard to tell], and revised one passage -- which revision did not however, speak to how many Balrogs actually existed.
And yet Tolkien does
not revise other texts that still refer to very many Balrogs. Why not? When I look at all of them, some might be explained by saying that he simply didn't get around to them, but I'm not sure that necessarily works perfectly for all examples.
And since there are seemingly more edited Silmarillion readers that HME readers, many do not realize that it was Christopher Tolkien, not JRRT himself, who edited the pasages in question. This often enough 'complicates' the discussion, especially since Christopher Tolkien did not edit the War of Wrath passage in this respect, which often enough gets raised in the discussion.
That is, Silmarillion-readers-only do not necessarily know that the War of Wrath passage was written well before the marginal note, nor that Christopher Tolkien has edited other reference where his father did not.
And as this marginal note is not part of the text proper, was Tolkien going to truly give a specific number in the tale itself? And if so, three or seven? Or was JRRT just going to revise all the passages concerned to make the matter ambiguous -- while not refering to large numbers at least.
And while Tolkien did write another, this time certainly 'late' note, that the duel with Glorfindel and the 'demon' may need revision, that in itself does not tell us that the revisions were going to let the reader know how many Balrogs actually existed.
Revise what? Add a shadow? Make this Balrog more powerful? Shorten it? Since Tolkien wrote demon and
seems to 'avoid' Balrog in this late text, was he going to have Glorfindel fight a notable demon if 'lesser than Balrog' kind of demon -- hardly seems likely to me after all the external history behind Glorfindel slaying a Balrog, but I have read someone argue this possibility nonetheless.
So it can get
'a bit' complicated in my opinion