1. Harry Ransom Center, MS 3327, Container 196 DS ID: DS3982 Title: Papal bull Author: Sixtus IV Place: Italy and Rome Date: 1474 February 7
2. Newberry Library, VAULT folio Case MS 150 DS ID: DS18203 Title: Indulgence and Letter Author: Catholic Church and Sixtus IV Place: Florence and Italy Date: 1481 April 25.