Here is my (Elbowin's) bold pick on Narjot:
I think of it as a derivation from the name Narses (borne by a byzantinian general fighting against the Goths in Italy). Narses shows in italian as Narseo, and the sound shift s->j is typical for northern italian dialects (some examples made it into standard italian: Paris [the city] -> Parigi, partisan ->partigiano, parmesan -> parmigiano).
I also thought of arabic Narjis because of the crusade connection to the holy land, but I think this explanation is less plausible.