Interesting.
Is the Catechism supposed to be something infallible?
The pre-Vatican 2 catechism is not infallible by itself, since it can be subject to change, but it defines at whatever time the things that a Catholic is required to believe in order to be a member of the church. Therefore when changes are made to the catechism, the definition of Catholic is changed, and throughout history when heresies and error became official, to formally counter those heresies, the Catechism would include the "Catholic" opinion on the matters they pertain to.
So is the catechism infallible? it IS as far as it contains opinions in union with various popes who spoke Ex-Cathedra on a subject. It is not infallible when the pope is a heretic himself, and promulgates an opinion which is not "Catholic" as Catholicity has been understood in its near 2000 year history.
So the definition of "Catholic" can change with time, for the removal of heresy, in order that "discovered religion" will be known in greater purity, and the overall CCC will contain less errors and more truth.
What the Catholic church up to Vatican 2 considered "discovered / revealed religion" was along the lines of the qualities of those who were made Catholic saints, who by miracles attributed to them, proved that they enjoy the favour of God, and logically that their beliefs on various matters contain the truth, which true religion must always incorporate into its doctrine.