Marie-Jose Tubiana's "Un document inédit sur les sultans du Wadday" is a useful article for anyone interested in the history of Waday. Consisting of 2 similar documents attributed to a Usman ibn Fodde or Uthman ibn Fodda, the translated source is a chronological list of the sultans of Waday. In addition to collating 2 versions of this source, one of which came from the sultan of Waday, Tubiana uses other sources to corroborate and comment on the list. Like the Diwan of Kanem-Borno, it's basically a list of the sultans with a few sentences describing what the said ruler accomplished or experienced during his reign. In addition, there is some confusion in the source as it incorrectly places Sabun into an earlier chronological moment in the history of Waday.
Despite some of the obvious problems of the source, it's chronology seems to be generally accurate. Like, perhaps, the Diwan of Kanem-Borno, there may be some mystical value to certain numbers attached to reign lengths (66, for instance, was special in this source) and the earlier kings appear to have existed in a more "mythical" context. Sadly, what actually transpired between Abd el-Karim and the Tundjur kings who ruled previously is not entirely clear. One is still unsure about Abd el-Karim's connection to Bidderi in Bagirmi, too. All one can say is that Abd el-Karim probably reigned sometime in the first half of the 17th century and he was a propagator of the Islamic faith. Subsequent rulers are also mentioned but it is mainly only beginning with Sabun in the early 19th century are the events of Waday's political history better known. The wealth of sources for the 19th century allows for more corroboration and detail on the kings of Wadai, while the events of the years prior to Sabun can only be glimpsed with occasional references to the Tunjur, Darfur or the larger Central Sudan. Indeed, even the origins of Abd el-Karim are unclear as some source ssuggest roots in the modern-day Sudan while other traditions, such as those reported by Barth and Nachtigal, suggest some kind of connection to the Islamic settlement of Bidderi and a Muslim movement against the pagan Tunjur.
Interestingly, some later research suggests some degree of Islamic observance among the Tunjur. In fact, the Tunjur rulers were remembered by Arab names, including the final one, a Dawud, who was overthrown or replaced by Abd el-Karim. In addition, O'Fahey cited evidence of a Tunjur king from the region of Darfur and Wadai who was reported in Muslim sources. To what degree Abd el-Karim was the first Muslim ruler in what became Waday is difficult to say, but the realities of Tunjur, Kanem, and Bornoan influences in the region suggest Islam may have had some influence in Waday before the 17th century. Later Borno influences and conflict with Borno, Darfur, Bagirmi, Rabeh, the Mahdists in Sudan, and, finally, the French, continued to shape Waday's sultans while a number of contenders, dignitaries, and rival claimants for the throne frequently clashed. Furthermore, some Waday rulers clashed with their own dignitaries who resisted kings who became too powerful. This frequent instability and conflict over power helps explain why Waday could occasionally rise to a hegemonic status in the Central Sudan but very quickly, within a reign or two, suffer severe declines, population exoduses, plagues, and even do nothing while Rabeh ravaged tributary states like Dar Kuti, Dar Runga and Bagirmi.