A fact from September 1503 papal conclave appeared on Wikipedia's Main Page in the Did you know column on 27 July 2009 (check views). The text of the entry was as follows:
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This is, at the moment, a one-source entry, relying totally on Baumgartner. Baumgartner is the only scholar or source that says that there were thirty-nine cardinals present. The Venetian Ambassador at the Conclave, Foscari, gives a list of thirty seven present, and eight absent (in Marino Sanuto). Giovanni Burchard, who was there at the Conclave as Papal Master of Ceremonies, and who kept an official diary, reports in that diary that thirty-seven cardinals attended. Onuphrio Panvinio, who was a friend of Pope Marcellus II and worked in the Vatican Library when Marcellus was Librarian (1548-1555), also says that there were thirty-seven in attendance and eight absent. In the light of these primary sources, something more is needed than the word of Baumgartner. Why is Baumgartner right, if he is right, and who are the two additional cardinals?