“The article suggests the pope has only exercised this “authority” only twice. Are there no others?”
Actually it says, “ You can count on one hand (two fingers, even!) the number of times the pope has invoked this authority since 1800 A.D.”
Twice since 1800.
Is the source you provided an official roman catholic site...that is one approved of by the vatican?
Or is it just somebody's blog site. Perhaps yours??
Is this just his own personal opinion?
What makes his blog official? Why should it be accepted?
Regarding historical papal documents, Catholic theologian and church historian Klaus Schatz made a thorough study, published in 1985, that identified the following list of ex cathedra documents (see Creative Fidelity: Weighing and Interpreting Documents of the Magisterium, by Francis A. Sullivan, chapter 6):
Tome to Flavian, Pope Leo I, 449, on the two natures in Christ, received by the Council of Chalcedon;
Letter of Pope Agatho, 680, on the two wills of Christ, received by the Third Council of Constantinople;
Benedictus Deus, Pope Benedict XII, 1336, on the beatific vision of the just after death rather than only just prior to final judgment;[76]
Cum occasione, Pope Innocent X, 1653, condemning five propositions of Jansen as heretical;
Auctorem fidei, Pope Pius VI, 1794, condemning seven Jansenist propositions of the Synod of Pistoia as heretical;
Ineffabilis Deus, Pope Pius IX, 1854, defining the Immaculate Conception;
Munificentissimus Deus, Pope Pius XII, 1950, defining the Assumption of Mary.
There is no complete list of papal statements considered infallible. A 1998 commentary on Ad Tuendam Fidem issued by the Congregation for the Doctrine of the Faith published on L'Osservatore Romano in July 1998[77] listed a number of instances of infallible pronouncements by popes and by ecumenical councils, but explicitly stated (at no. 11) that this was not meant to be a complete list.
https://en.wikipedia.org/wiki/Papal_infallibility