The quotes come from the
Fall of Gondolin, which was begun in 1916, while Tolkien was recuperating from the Somme. It doesn't appear in the published
Silmarillion, but is directly referenced in it: the Silm has a line about how 'much more is told in the Fall of Gondolin' (it's the line that references Ecthelion killing Gothmog), but doesn't go into any detail. It will almost certainly be published in this year's
Fall of Gondolin standalone novel.
It's worth remembering that the published
Silmarillion is a chimera of different sources, cobbled together by Christopher Tolkien after his father's death. There's a book called
Arda Reconstructed which goes into exactly where every piece of the Silm came from; I've not read it, but I'm pretty sure the Fall of Gondolin section stands alongside the Nauglafring chapter as being written almost entirely by Christopher to cover a gap in the Professor's
Quenta Silmarillion.
It's impossible to know how Tolkien would have finished the (post-LotR) story in
Unfinished Tales referred to as 'Of Tuor and his coming to Gondolin'. However, 'Of Tuor...' and the 1916 'Fall' both share the same attention to detail, particularly in how the list of the gates of Gondolin in 'Of Tuor...' mirrors the list of the noble houses in the 'Fall'; I suspect Tolkien was inspired by the Welsh tale of 'The Dream of Rhonabwy' in this, though I have no proof.
Point is, they were definitely written in similar styles, and at times 'Of Tuor...' directly follows the older story, so we shouldn't think Tolkien actively rejected it.
hS