To prove the Christ is Son of David, you need the lineage records. These were lost when the Romans ruined the Temple. I Herod the Great ruined the records because he was not of pure Jewish blood, and had no right to be king of the Jews (he bought his rule from the Romans) and did not want his right to be king to be questioned.
Besides, you have no "tribes" now; how do you know who the sons of David are, anyway?
Besides, you have no "tribes" now; how do you know who the sons of David are, anyway?