[Galin]

Originally Posted by William Cloud Hicklin

Galin, Without getting into a 'my canon is better than your canon' fight, ...'

In which battle The Lord of the Rings is mighty strong but there is another approach in any case.

'... post-LR Tolkien definitely included the 'sylvan' Elves of Mirkwood and Lorien among the Eldar, coining the term Nandor for them and making them cousins of the Laiquendi of Ossiriand. Under that understanding, the "East-elves" are somewhere, well... farther East.'

Not necessarily. The Silvan Elves of Mirkwood and Lórien can still be East-elves and not Eldar when later (but 'unpublished') texts are considered.

'The Silvan Elves (Tawarwaith) were in origin Teleri, and so remoter kin of the Sindar, though even longer separated from them than the Teleri of Valinor.' (...) 'The Silvan Elves hid themselves in woodland fastnesses beyond the Misty Mountains, and became small and scattered people, hardly to be distinguished from Avari; but they still remembered that they were in origin Eldar, members of the Third Clan, and they welcomed those of the Noldor and especially the Sindar who did not pass over the Sea but migrated eastward [i.e. at the beginning of the Second Age].' Unfinished Tales

The Tawarwaith were in origin Teleri, hardly to be distinguished from Avari (which thus distinguishes them actually), and were in origin Eldar.

'Nandor. This name must have been made at the time, in the latter days of the March, when certain groups of the Teleri gave up the March; and it was especially applied to the large following of Lenwe who refused to cross the Hithaeglir. The name was often interpreted as 'Those who go back'; but in fact none of the Nandor appear to have returned, or to have joined the Avari. Many remained and settled in lands that they had reached, especially beside the River Anduin; some turned aside and wandered southwards'. Q&E

So, Mirkwood and Lórien: mostly 'East-elves' (The Lord of the Rings). The East-elves were probably a mix of Nandor (Eldar 'in origin') and Avari. The term Eldar becomes narrowed again to basically West-elves (it had been narrowed already in the internal history). This is not only a possible explanation (in my opinion), using both The Lord of the Rings and unpublished texts, but I note an earlier situation with respect to the Danas revealed in The History of Middle-Earth:

'In any case, the Danas are sufficiently characterised as Elves of the Great March who abandoned it early on but who still felt a desire for the West (...) Their position is anomalous, and might equally well be classified either as Eldarin or as not Eldarin.'

Christopher Tolkien, commentary The Lhammas HME V