Elsewhere, as at Dura-Europos, Mithraic graffiti survive giving membership lists, in which initiates of a mithraeum are named with their Mithraic grades. At Virunum, the membership list or "album sacratorum" was maintained as an inscribed plaque, updated year by year as new members were initiated. By cross-referencing these lists it is possible to track some initiates from one mithraeum to another; and also speculatively to identify Mithraic initiates with persons on other contemporary lists such as military service rolls and lists of devotees of non-Mithraic religious sanctuaries. Names of initiates are also found in the dedication inscriptions of altars and other cult objects. Clauss noted in 1990 that overall, only about 14% of Mithraic names inscribed before 250 CE identify the initiate's grade – and hence questioned the traditional view that all initiates belonged to one of the seven grades. Clauss argues that the grades represented a distinct class of priests, "sacerdotes". Gordon maintains the former theory of Merkelbach and others, especially noting such examples as Dura where all names are associated with a Mithraic grade. Some scholars maintain that practice may have differed over time, or from one Mithraeum to another.