The second division

The Division of Tongues acts as an introduction to the grammatical treaty of elvish languages, Tengwesta Quenderinwa, laying foundation to their relation to each other. Its final version showed a layer of revisions, intended to incorporate the conceptual shift from Noldorin to Sindarin, but that work was left incomplete. The second of listed divisions is concerned with Nandor that underwent a back-and-forth in terms of their identity on multiple occasions.

In the original version TQ1 they are presented as belonging to the second clan:

[…] the followers of Nano (or Dan) forsook the main host of the Noldor upon the march […] These are the Pereldar, or 'Half-eldians', or the Danian Elves, […] Who were also in Ossiriand called the Laiquendi or Green Elves.

But in the TQ2 that was changed to the third clan:

the followers of that lord that is named Nano or Dân forsook the hosts of the Teleri upon the long march […] These are the Nandor, or Danian Elves […] Who were also in Ossiriand called the Laiqendi or Green Elves.

This idea stays around for a decade, as told also in the Quendi and Eldar, where it became a critical point in the etymology of Lindon:

this people still called themselves by the old clan-name *Lindai […] The country in which most of them eventually settled, as a small independent folk, they called Lindon.

But another decade later Tolkien has restored the old narrative, this time with a twist. In Silvan Elves and Silvan Elvish he writes:

For the most part these secessions were made by groups of the Lindar […] The Eldar of Ossiriand, the Green Elves, […] were probably in origin of Noldorin kinship. The Wood-elves of the time of the War of the Ring appear to have been those of Teleri and their descendants who were dismayed by the Hithaeglir.

This time Green Elves and Silvan elves became separate people, at least explicitly so. In fact, the second division itself is described now not as a singular decision, but a multiple smaller groups abandoning the host before crossing the Misty Mountains. That allows for those elves to be of various origins. In fact, we can see this concept emerging already in Quendi and Eldar, where the elves of the Vale of Anduin are described as a mixed folk of Teleri origin, including Lindarin Avari.

Re-appearing Noldorin roots of Nandor was not a one-off idea, however, briefly seen again in the Eldarin Hands, Fingers and Numerals:

the Nandor were in origin a detachment of the Noldor that went astray and did not come into Beleriand until shortly before the Exilic period.

Despite that, his latest writing The Rivers and Beacon-hills of Gondor reverts in full to the early 50s:

There, especially near the Hithaeglir (on either side), they found scattered settlements of the Nandor, Telerin Elves who had in the First Age never completed the journey to the shores of the Sea.

To summarize:

Date	Source	Nandor origin	Silvan elves origin
1937	Tengwesta Quenderinwa	Noldor	= Nandor
1951	Tengwesta Quenderinwa	Teleri	= Nandor
1959	Quendi and Eldar	Teleri	Avari
1968	Silvan Elves and Silvan Elvish	Noldor	Teleri
1968	Eldarin Hands, Fingers and Numerals	Noldor	not mentioned
1969	The Rivers and Beacon-hills of Gondor	Teleri	= Nandor