But then how do you explain newly formulated dogmas (beliefs)? The original Church did not "know" the dogma of Papal infallibility or of Imamuclate Conception or of the Purgatory.
Again, using the Maronite tradition to address this question, here is the explanation.
Although the Fathers of the early Church, including St. Ephrem, attest to the reality of the soul's need for purification after death, the widely known term purgatory is not explicitly stated in the Scriptures. The term comes from Western Tradition, and did not even appear until the 11th century at the earliest. Since the 16th century the Catholic Church officially teaches that the departed stand in need of purification from whatever keeps them from full union with the Trinity in the Kingdom and is wisely silent about further details. Remember that what is being described is a state of the soul, not a place.
Catholics believe that no new truths have been given by anyone but Jesus, the full Revealer of God's Truth; yet, the explanation of this revelation grows and develops, according to our historical time and growth in knowledge and as the Holy Spirit allows us to see these things afresh.