Tolkien's final First Age timeline

[Tar Elenion]

Originally Posted by Arvegil145

I'm aware that the table dates from the end of 1959, but I could've sworn that there's another place which dates the Elmo-Galadhon-Celeborn family tree to the late '60s, but my brain isn't cooperating...

I keep thinking that too, but now I am wondering if it might be this:
"On the second of these late additions to the typescript, the birth of Eldún and Elrún in the year 500, see pp. 257 and 300, note 16."