Annuario Pontificio
…recognized the decisions of the Council of Pisa (1409), listing three popes for the period: Gregory XII (1406–1409), Alexander V (1409–1410), and John XXIII (1410–1415). The Western Schism was reinterpreted when Pope John XXIII (1958–1963) chose to reuse the ordinal XXIII, citing "twenty-two Johns of…