Wait a minute, what gives you this idea? Because I ask for evidence for something from an apostolic source, it negates tradition? So in other words, anything that anyone claims is apostolic tradition is automatically right, without any evidence that it comes from an apostle? Then why in the world did we condemn the Gnostics??
No, not anything that anyone claimed was Apostolic Tradition was automatically right,
precisely because, if it was not right, there would not be any evidence that it came from an Apostle. What I mean by that is this: the Apostles taught the faith to many people throughout the Mediterranian. The faith that they taught those people was all the same. Therefore, when the Apostles died, they left behind a large group of people who had all been taught the same thing, and a few of them had been appointed directly by the Apostles as their successors (e.g. Timothy, Titus, Linus, Ignatius of Antioch, etc.). This group of people was “the Church.” As such, if someone (or a group of people) introduced a new teaching, claiming it was of Apostolic origin (and sometimes with accompanying writings such as in the case of the gnostic gospels), the Church rejected it for the very reason that it was not something that had been believed and taught by the Church as a whole from the time of the Apostles. This is why the gostics were condemned, because they tried to introduce new teachings that had never been taught before, even attributing some of their gospels to Apostles (such as the Gospel of Philip).
On the other hand, for the same reason, this is why the IC (since you used it as an example) was accepted. It was a belief held in common by the Church from the beginning, and we have the historical writings to prove it. Just because none of those writings were ultimately chosen to be included in the canon of scripture does not mean that the belief was false and not of Apostolic origin. As explained by Jimmy Akin in his book
The Fathers Know Best (Introduction to chapter 49):
The Fathers of the Church taught that Mary received a number of distinctive blessings in order to make her a more fitting mother for Christ. These included her role as the New Eve (corresponding to Christ’s role as the New Adam), her Immaculate Conception, her spiritual motherhood of all Christians, and her Assumption into heaven. These gifts were given to her by God’s grace. She did not earn them, but she possessed them nonetheless.
The key to understanding these graces is Mary’s role as the New Eve, on which the Fathers were quite clear. Because she is the New Eve, she–like the New Adam–was born immaculate, just as the first Adam and Eve were created immaculate. As the New Eve, she is mother of the New Humanity (Christians), just as the first Eve was the mother of humanity. And, as the New Eve, she shares the fate of the New Adam. Whereas the first Adam and Eve died and went to dust, the New Adam and Eve were lifted up bodily to heaven.
Even before the terms “original sin” and “immaculate conception” had been developed, early passages imply the concepts. Many works mention that Mary gave birth to Jesus without pain. Pain in childbearing is part of the penalty of original sin (Gn 3:16), thus, Mary could not have been under that penalty. By God’s grace she was made immaculate in anticipation of her Son’s redemptive death on the cross. The Church therefore describes Mary as “the most excellent fruit of redemption” (CCC 508).
I have to go right now, but later I can provide you with some of the quotes from these works (which begin as early as 90 A.D.) that either explicitly or implicitly speak of Mary’s sinless nature.
The point though is that this belief was accepted by the Church because it was in line with what the entire group of people had been taught by the Apostles.
