Distinctiones
21.1, 67.20: Gratian himself makes some observations on the numerous names given to those who monitor priests and are subject to the pope, those whom we usually call "bishops": "Inter eos quedam discretio seruata est, ut alii appellentur simpliciter "sacerdotes," alli "archipresbyteri," alii "corepiscopi," alii "episcopi," alii "archiepiscopi" seu "metropolitae," alii "primates," alii "patriarchae," alii "summi Pontifices." The same observation could be made about those found between bishops and priests or deacons.

50.6, 179.15: Pope Nicolas I (858-867) writes a letter to Chorbishop Osbald of Quadrantinus
50.38, 194.36: another letter from N to O, though most manuscripts call him "co-bishop" rather than "chorbishop"

64.1, 247.31: Gratian himself mentions the ordination of chorbishops as if it were still normal and occurring.

67.1, 253.20: again, on the ordination of chorbishops, from Ps-Anacletus (Isidore?)

68.3, 254-55: bishops must be ordained in cities but chorbishops can be ordained in towns (in vicis); bishops have the right of consecration but chorbishops can only ordain minor orders, not deacons or priests
68.4, 255: In what ways chorbishops and bishops differ (#2)

68.4.3: Gratian notes that chorbishops are today banned from the church.

69.1, 256.31: with permission of the bishop, it is allowed chorbishops to "promouere lectores" ?

95.1, 331.38: Refers back to D. 68, Quamvis corepiscopis
 
 

De consecratione, 1294.11: chorbishops should consecrate churches or vessels
 (taken from Burchard)