Romans, bud, I love you; but your perseverating on this indicates that you have completely missed the point of my post’s first paragraph.
Let me try to rephrase my point.
Descendancy is not exclusive. The fact that one is literally descended from a person who lived thousands of years ago through one line, does not mean that one is precluded from also being descended from that ancestor’s sibling through another line. In the House of Israel, tribal membership was primarily an indicator of subcultural identity, covenant obligations, and specific sets of inherited blessings. If Lehi had grown up considering himself (say) a Levite, then looking at an actual family tree that confirmed he also had Josephite ancestry would have been meaningful to him in light of Jacob’s deathbed blessing upon Joseph and his posterity.