Regarding when exactly Ugaas as a specifically Somali appropriated traditional title distinct to Goyta/Get'a/Gaz'a as a rewarded Harari Adalian imperial title would have taken place, for this my only hypothesis at this point would be Marehan oral history.
Essentially one of the top 3 most consequential moments in Marehan oral history is the saga concerning the change from "Garad" to "Ugas" as the title of kinship with an internal coup by a cadet branch that successfully displaced the ruling housing. The ruling house was the Reer Garad of Garaad Hiraabe (using the title of Garad as investiture) who then became the last "Garad" title within Marehan. The cadet branch that came into power were the Hussein Yusuf Matan who then elected to invest with a new title of "Ugaas." This house is today still with investiture devolved down to the Reer Ugas Shermaarke.
Now the Reer Garaad and even Hiraabe is memorialized in Marehan oral history as the ruling house of the clan with the title of Garad as investiture. And this Hiraabe and ruling branch of Marehan in the oral history is then miraculously corroborated being recorded in the Conquest of Abyssinia as the chief of Marehan. His family is recorded as the only Somali rewarded with the Adal honorific "Goyta."
When you bridge oral history and the written record the logical hypothesis presents itself that the birth of "Ugaas" is probably quite similar to the development of "Ceasar" (later Kaiser/Czar). Namely the honorific name of Julius Caesar itself became the title of investiture post Julius Ceasar. The Roman title during his life was Dictator!
All of this holistically reinforces the probability that the upstart Marehan cadet branch decided to break with the memory of the Garaad title so synonymous with the kin they displaced for chieftaincy that they then, essentially, appropriated the honorific Adal imperial title which had been rewarded to their ruling family, or the title of Goyta, itself being a very powerful entitlement buttressed by its prestigious usage in the land of Adal important to the Somali countryside at large.
And thus Goyta became like Ceasar to come to be known in the modern era as Ugaas like Czar!
Goyta - Geta - Gez'a - Ag'aze - O'gaz - U'gaas
