Gianfranco Contini, list of loci critici of the Roman de la rose.
Florence, Fondazione E. Franceschini – Archivio G. Contini, S4.F192.9

The presence of shared innovative readings in two or more manuscripts can indicate the existence of a lost common model (i.e., the copy in which the innovation was first introduced).

Image courtesy of Fondazione Ezio Franceschini.