'The Elves far back in the Elder Days became divided into two main branches: the West-elves (the Eldar) and the East-elves. Of the latter kind were most of the elven-folk of Mirkwood and Lorien; but their languages do not appear in this history, of which all of the Elvish names and words are of Eldarin form.* (footnote) *In Lorien at this period Sindarin was spoken, though with an 'accent', since most of its folk were of Silvan origin (...) But Lorien, Caras Galadhon, Amroth, Nimrodel are probably of Silvan origin, adapted to Sindarin.'
And the second quote is from Appendix F, where Eldar is said to refer to the three kindreds who sought for the Undying Realm '... and came there are the beginning of days, save the Sindar only' Meaning (as I take it) the Eldar are those Elves who passed Oversea, plus the Sindar -- basically the West-elves -- with the Sindar making it to Beleriand, a very 'Western land' of course, in ancient days.
I note Christopher Tolkien's entry for Eldar as later published in The Children of Hurin: Eldar The Elves of the Great Journey out of the East to Beleriand. I think (if I recall correctly) Christopher Tolkien wrote something else in Children of Hurin that seems to agree with The Silmarillion (concerning the term Eldar), but in my opinion this much agrees with The Lord of the Rings well enough, if we read it as 'at least to Beleriand'...
... as I doubt the intended meaning here does not include those Elves who passed Oversea!
I think Amroth's words are interesting here too, although Tolkien himself did not publish this however. Amroth tells Nimrodel that it is said: '... the grace the Valar gave to us to pass over the Sea is granted also now to any of those who made the Great Journey, even if they did not come in ages past to the Shores and have not yet beheld the Blessed Land.'
Or considering The Lord of the Rings, I think this could be read as: even if they are not Eldar or West Elves -- this being spoken to Nimrodel, a Silvan Elf. This was a late text in any case: Amroth And Nimrodel, dated around 1969 or later...
Wherein Amroth, a Sindarin Elf... is seemingly golden haired!
