Information on differentia
In the original Cantus index, differentiae were assigned two-digit codes, where the first letter indicated the last pitch of the differentia and the number distinguished between differentiae of the same mode had the same last pitch. The same codes were used for the indices of B-TO olv 63, B-TO olv 64, and NL-DHk 70 E 4.
de Loos, Ike. Inventory of Tongeren, Onze-Lieve-Vrouw-Kerk (Our Lady's Church), 64 (olim IV). Edited by Andrew Mitchell. In: Cantus Manuscript Database for Latin Ecclesiastical Chant: Inventories of Chant Sources. Directed by Debra Lacoste (2011-), Terence Bailey (1997-2010), and Ruth Steiner (1987-1996). Web developer, Jan Kolácek (2011-).