[William Cloud Hicklin]

But how are we to interpret "west-elves" and "East-Elves?" I'm not aware of any line on the map, but I feel comfortable that "the West-lands of Middle-earth" extended beyond the Hithaeglir. Rather like Ostrogoths and Visigoths- the West-goths were the ones who moved west first, even if many of their 'eastern' cousins eventually reached Western Europe as well. Similarly the West-elves/Eldar were those who left Cuivienen for the West, leaving their Refusenik brethren behind.

It's also worth observing that, although of course they occurred more or less by accident, Elvish place-names in The Hobbit such as Esgaroth are 'Ilkorin,' that is, the tongue of the Grey-elves under the old dispensation: a language which Tolkien derived (in theory) from Common Eldarin, not Primitive Quendian. This would suggest that the 'west-elven language group' extended at least as far as Erebor and the Sea of Rhun.

Or, from another angle: Tolkien tells us that there were no Avari in Beleriand (notwithstanding his vacillation with regard to Eol). Therefore the Green-elves were Eldar; and if they were then necessarily so also were the Danian Nandor.