Tolkien's final First Age timeline

[Galin]

Originally Posted by Aiwendil

In fact, we know that by about the time of the writing of "The Shibboleth of Feanor", Tolkien had either rejected or forgotten* much of what he had developed over the course of the many "Time and Ageing" texts of c. 1959, since in the two texts given in ch. XIX, "Elvish Life-Cycles", he presents a completely different approach to Elvish longevity in the form of cycles of renewal.

Well, that's what I get for skipping around! Hadn't read XIX yet (still haven't read XX) even though I've jumped to much later sections of the book. As I say, I'd been aware of the nette remark since Vinyar Tengwar, and indeed, looking at text II in XIX for example -- erm, now that you point it out --

Elves lived in life-cycles? sc. birth, childhood to bodily and mental maturity (as swift as that of Men) . . ."

So, so far, for me, still going with the external chronology and the nette description.