What impact did the False Decretals have on Gratian's collection of Canon law? In the ninth century, a series of elaborate forgeries were written under the pseudonym of Isidore Mercator, which are now known as the Pseudo-Isidorian Decretals (or simply the False Decretals).  Among these documents are over 100 letters ostensibly written by popes and bishops in the early church, in which these popes and bishops repeatedly quoted works written centuries after their lifetimes.

Everett Ferguson indicates that this was no small thing:


  This collection became the most influential forgery in the history of the Roman Catholic church.  It became the basis of the claims for the papal monarchy in the later Middle Ages. (Church History, 18.IV.B)


This is obviously a sensitive subject, and doubly so because the gradual discovery of the fraud occurred during the Reformation period, during which the RCC faced broader challenges to its authority.  Nonetheless, I'm hoping that it's possible to politely probe the influence of these documents on the medieval church.

One particular point of disagreement I seem to have uncovered relates to the decretals' impact on the Decretum Gratiani (or Concordia discordantium canonum), an important 12th-century collection of canon law.  Wikipedia seems to downplay their impact on Gratian's work, not listing the False Decretals as one of his sources, and saying that his work "ended the immediate influence of the False Decretals" (source).

At the same time, the Catholic Encyclopedia notes that "many fragments" of the false decretals "are to be found in the 'Decretum' of Gratian."

Thus I'd like to limit my query here to the impact of the Pseudo-Isidorian Decretals on Gratian's Decretum.  Ways of viewing "impact" might include:


the percentage of Gratian's text that, directly or indirectly, comes from the False Decretals
the percentage of Gratian's supporting references that ultimately come from the False Decretals
any instances of statements or rules that Gratian rests solely or primarily on the False Decretals


Note that I am framing this as something that is, at least theoretically, objectively answerable.  I'm specifically not asking how much of Gratian's text ought to be kept or discarded, for example, nor do I care how Catholics and Protestants have defended or attacked the legitimacy of Gratian's collected canons.  Instead, I'm interested in a textual analysis of the use (intentional or unintentional) of the Pseudo-Isidorian Decretals in the Decretum Gratiani.
I will try an answer based on the one source I found online with a quick search. My answer relies on the summary in the review [2] on the book [1]. The whole book [1] gives more details. If someone has special questions in the comments and I have time, I will search it in the library. 



The Pseudoisodorian Decretals were important for Gratian. 400 out of 4000 chapters of the Decretum Gratiani were "pseudoisidoric" ("psedoisidorianisch"). 220 of them deal with processual matters. For the justification of the papal primate Gratian used Pseudoisidor "fewer" ("weniger"). The direct sources of Gratian for these cittations are less clear.



[1] Fuhrmann, Horst: Einfluß und Verbreitung der pseudoisidorischen Fälschungen. Von ihrem Auftauchen bis in die neuere Zeit. (Schriften der Monumenta Germania« histórica 24, I-IIΙ.) Anton Hiersemann, Stuttgart 1972—1974.
(title in English: Influence and distribution of pseudoisidoric counterfeits. From their emergence to newer times; 3 Volumes, intersting is here esp. Vol. 2)

[2]  Landau, Peter: Horst Fuhrmann, Einfluß und Verbreitung der pseudoisidorischen Fälschungen. Von ihrem Auftauchen bis in die neuere Zeit. In: Zeitschrift der Savigny-Stiftung für Rechtsgeschichte. Kanonistische Abteilung, 1975, Vol.61(1), pp.377-392 (388f.). (buyable online)