So, we know what the traditions taught by the epistles are. But are there additional traditions that the apostles taught by word, and, if so, how do you prove the traditions not written down were actually taught by the apostles?"As I have already observed, the Church, having received this preaching and this faith, although scattered throughout the whole world, yet, as if occupying but one house, carefully preserves it. She also believes these points [of doctrine] just as if she had but one soul, and one and the same heart, and she proclaims them, and teaches them, and hands them down, with perfect harmony, as if she possessed only one mouth. For, although the languages of the world are dissimilar, yet the import of the tradition is one and the same."
Nice quote, doesn’t answer the question.