: Says who? Elrond is descended from them as is Celebrian, and Amroth if you take him as Galadriels son.

Elrond is half-elven and doesn't count. Celebrian is Galadriel's child and moreover she was probably born during the Second Age, not the first.

And as for Amroth, no I don't take him s Galadriel's son since something as important as that would have been mentioned in LotR...

: Maglor, Caranthir and Curufuin were all married, an Chris Tolkein himself reports that his father said 'we never meet the progeny of Feanors sons' whilst debating the parentage of Celebrimbor.
: There could feasibly exist other offspring who do not enter the tales but nonetheless exist

Indeed, nonetheless they didn't enter the tales and thus they don't exist *in* the tales... And I know of no other way to measure their existence.

Aris Katsaris