Edain/Eldar marriages

I was rereading Appendix A Section I The Numenorean Kings in The Return of the King and I came to the part where it explains the three unions of the Edain and the Eldar: Luthien and Beren; Idril and Tuor; and Arwen and Aragorn. When I read this I was curious why it would say only three. Unless I am mistaken there are four, they left out Nimloth and Dior. Nimloth was clearly an elf with Celeborn as her uncle, unless her mother was a human, (which is never even implied,) and she is clearly said to be an Elf-maiden of Doriath. And Dior is a half-elf being the son of Beren and Luthien.

If you can spread some more light on this subject for me I would be greatful.

I also have one question on the marriage of Idril and Tuor. Since Tuor and Idril sailed off into the sunset, and their deaths were never recorded, did Idril sacrifice her immortality for Tuor? I think she would have to since Luthien and Arwen both did also, but I don't remember actually ever reading it through-out all the books.

Thanks again if you can help me on any of these or even point me in the right direction.