According to the geonim Ẓemaḥ and Saadia, Ukban, when he was young, was wont to curl his hair, his surname "de-Ẓuẓita" being derived from that habit.
As to the nature of Ukban's sins and repentance[3] Rabbi Aḥai of Shabḥa, in his "She'eltot" (sections "Wa'era" and "Ki Tissa"), tells almost the same story as Rashi, of a man who was called "Nathan de-Ẓuẓita," but without mentioning either that he was likewise called "'Ukban" or that he was an exilarch.
It may therefore be assumed either that there were two Nathan de-Ẓuẓitas, the second being identical with the exilarch Ukban b. Nehemiah, or that Joseph b. Ḥama must be understood as comparing Ukban, in his repentance, to Nathan de-Ẓuẓita, who was much earlier and, perhaps, was not an exilarch.
It is true that in the Seder 'Olam Zuṭa it is clearly affirmed that Nathan I was called also "Ukban"; but in other details the three recensions of that work disagree with Joseph ben Hama, in that they leave it to be supposed that Nathan de-Ẓuẓita was the son of Anan and not of Nehemiah, and that they represent him as the father of Huna the exilarch, who lived in the time of Judah ha-Nasi I.
The Seder 'Olam Zuṭa has in its list three exilarchs called "Nathan," the second being the grandson of the first, and the third the son of Abba ben Huna and father of Mar Zuṭra; it is the chronology of Nathan III that coincides with that of another Ukban.