Pseudoisidore Cluny

In 1963, Horst Fuhrmann argued that three copies of the A1 recension of the False Decretals are so closely related that they must go back to a common source, and suggested that this was a copy made in Cluny around the year 1000. The oldest of the three codices, namely Paris, BnF, nouv. acq. lat. 2253 (saec. XII), was written in Cluny.

With the discovery of New Haven, Yale University, Beinecke Library, 442 as a mid ninth-century copy of the Cluny recension, its role in understanding the Pseudoisidorian forgeries changed significantly. As Knibbs put it (https://pseudoisidore.blogspot.com/2010/03/introductory-iv-varieties-of-pseudo.html?m=1):

Until the 1970s, everyone thought that this was one of the later, unimportant versions. But then New Haven, Beinecke Rare Book and Manuscript Library, Ms. 442 turned up ... It now looks like this manuscript, from the mid-ninth century, gave rise to all the later medieval copies of the so-called Cluny recension (some of which ended up at Cluny, which is why we have this daft name for it). This book is exciting because it looks like it was assembled in the Pseudo-Isidore's workshop, perhaps even at Corbie.

Fuhrmann, Pseudoisidor in Cluny, https://www.mgh-bibliothek.de/dokumente/a/a080820.pdf