I was curious regarding how unbelievable it is that a being who was the father of many worlds would have actually chosen one group out of many. I have learned alot in pursuing that question.finally, I concluded that God "chose" Abraham before he was even born because of his nobility. One of his blessings once born was to sire the eventual vessel to house the very begotten son of God. Thereby, blessing all nations of this world.
So, ultimately person by person lineage is only important as to how it applies to redemption and return. So, Nephi is sufficed to know and share that he is a descendents of one of Jacob's sons.