The bull has never been authenticated by Rome. Quote a Vatican source or give it up.
Seems Rome has had a change of heart about this...amazing what a stroke of the pen can do.
I should note Roman Catholics place a lot of faith in other documents that are shall we say questionable.
We reproduce here the whole passage dealing with the Sabbatine privilege, as it appears in the summary approved by the Congregation of Indulgences on 4 July, 1908. It is noteworthy that the Bull of John XXII, which was still mentioned in the previous summary approved on 1 December, 1866, is no longer referred to (cf. "Rescript. authent. S.C. Indulg.", Ratisbon, 1885, p. 475). Among the privileges, which are mentioned after the indulgences, the following occurs in the first place: "The privilege of Pope John XXII, commonly [vulgo] known as the Sabbatine, which was approved and confirmed by Clement VII ("Ex clementi", 12 August 1530), St. Pius V ("Superna dispositione", 18 Feb., 1566), Gregory XIII ("Ut laudes", 18 Sept., 1577), and others, and also by the Holy Roman General Inquisition under Paul V on 20 January, 1613, in a Decree to the following effect:
http://www.newadvent.org/cathen/13289b.htm
The whole thing is a load of false teaching all around!