Since Anders Winroth and Carlos Larrainzar discovered earlier versions of Gratian’s Decretum, legal historians have explored these manuscripts for evidence that they hoped would reveal how Gratian’s changes and additions to his text could provide insights into how his thought and ideas developed.
Although there is still a vigorous debate about exactly how the manuscript tradition reflects the evolution of his Decretum, we know far more about Gratian now than we did before. Not everyone agrees on what we know. I think that Gratian began teaching in the 1120s, that the Saint Gall manuscript 673 is the earliest witness to his teaching, and that the other manuscripts discovered by Winrothand Larrainzar provide evidence that a version of his Decretum circulated widely in the 1130s. The final version of his Decretum ca. 1140 was compiled by gradually adding canons to various parts of the text over an extended period of time. That is an outline of what I think we know.
Kenneth Pennington, Gratian and the Jews, 31 BULL. MEDIEVAL CANON L. 111 (2014).