As I said there some flaws in this methodology, and even ancient writers notice it. for example:
"For it was customary in most families of note to preserve their images, their trophies of honour, and their memoirs, either to adorn a funeral when any of the family deceased, or to perpetuate the fame of their ancestors, or prove their own nobility. But the truth of History has been much corrupted by these laudatory essays; for many circumstances were recorded in them which never existed; such as false triumphs, a pretended succession of consulships, and false alliances and elevations, when men of inferior rank were confounded with a noble family of the same name: as if I myself should pretend that I am descended from M. Tullius, who was a Patrician,
and shared the consulship with Servius Sulpicius, about ten years after the expulsion of the kings." (Cicero, Brutus, 16.62)
Some modern historian (like Ronald Syme) seem to agree and claim that either the Nobilitas enter names to early consulate fasti of ancestors who never exist or falsely claim to have descended from families which by then were extinct.