There are far more than 2 ex cathedra decrees.  There have been 2 ex cathedra since the dogma of papal infallibility was defined by the First Vatican Council.  Additionally, de fide teachings are also infallible.  For example, the dogma of the Holy Trinity, the de fide teachings on the sacraments, etc., for example, that Christ ordained the 12 Apostles at the Last Supper is a de fide teaching of the Church.  It is a dogma that must be accepted and professed by Catholics. Those who deny it, or any dogma for that matter, are heretics.