Per the entry on The Consult.
Though the Gnostic Schools of Sohonc and Mangaecca are referenced as Far Antique contemporaries, the Mangaecca is the older of the two schools, as well as the one possessing the deepest Nonman affiliations—affiliations which would prove instrumental to the School’s transformation into the Consult.
And as for the entry on the Mangaecca.
Mangaecca—The ancient rival to the School of Sohonc, and last of the four original Gnostic Schools. From its founding in 684 by Sos-Praniura (the greatest student of Gin’yursis), the School of Mangaecca had pursued a predatory ethos, regarding knowledge as the embodiment of power. Though this earned the School an ambiguous reputation, the Mangaecca managed to avoid running afoul of the High Gnostic Writ, the edict of Nincama-Telesser circumscribing sorcerous conduct.
So it was not formed as a rival. The Mangaecca came first under Sos-Praniura, a student of Gin’yursis in 684. And the Sohonc later (around 400 years later) under Noshainrau. But they were great rivals after that.
Another minor note, though, of an odd timeline error in the glossary.
Noshainrau the White (c. 1005—72)—The founding Grandmaster of the Sohonc.
Outhrata (c. 1060—c. 1115)—Famed Sohonc metaphysician (and eventual Grand-master) who became a central figure in the so-called Gnostic Renaissance.
Titirga (c. 1055—c. 1119)—The second Grandmaster of the Sohonc, childhood pupil of Noshainrau the White, and the famed Hero-Mage of Ûmerau, reputed to be the most powerful sorcerer, Man or Nonman, to have drawn breath.
Noshainrau is the founding Grandmaster. Titirga is the second Grandmaster. And Outhrata is somehow eventually a Grandmaster, even though he died before Titirga was murdered?