Men of that era make the claim that the practice originated with the Apostles and their generation. This is something one wouldn't write if there was contrary evidence, or if people knew it was not true. If there was a "rule" regarding baptism that said "only adults could receive" that people knew about during that time, could Tertullian write that it was an "ancient practice"? When we say it comes from the Apostles, we mean it comes from that era of time. We presume that if some teaching is verified by an otherwise Catholic writer of the era, then it comes from the Apostolic teaching. The people reading these writings would have been aware of any false teachings - they had already heard the Apostolic teachings, both orally and written. They would be able to identify whether Tertullian was speaking truly.
This is like someone today writing about President Nixon. People would be able to verify whether Nixon did this or that. Thus, future readers would learn something about Nixon - presuming that the writer was not contradicted by other authors of that era. We don't see disagreement regarding infant baptism.
I take it that since I'm not the first to ask, that this is what Councils are for.
Councils are to verify what is the true teaching in the face of contradictory teachings. Thus, the Council of Trent verified Tertullian and Origen, etc., on the Church's practice of infant baptism in the face of the Anabaptists of the 1500's who were teaching the opposite.
Regards
There may have been no rule at all in actual practice and someone decided to invent one. Or, the actual practice could have been to Baptize only believers, as is the only case in the Bible, and someone decided to expand it. As you have said, any individual could have and did write error, as judged later. With the primitive communication network in use at the time, couldn't any teaching have spread from village to village as long as it was popular? And then, if a Catholic writer happened to like it and pick up upon it, it is then presumed to have been taught by the Apostles. To me, that is a lot of presumption.
This is like someone today writing about President Nixon. People would be able to verify whether Nixon did this or that. Thus, future readers would learn something about Nixon - presuming that the writer was not contradicted by other authors of that era. We don't see disagreement regarding infant baptism.
I've got another analogy for you. How about the Kennedy assassination? Many people had written very different things about it. Then, there was a "Commission" and a consensus was declared. Many people to this day believe the Warren Commission was a joke. The point is that no one can be sure what the truth is, even though it was "officially" solved. If translated to Catholicism, the Warren Report would have been declared infallible, and anyone disagreeing with it would have been a heretic. No room for disagreement or further study.
Writers on Kennedy enjoyed modern day free speech rights, and the inexpensive ability to publish on a grand scale. What was it like for ancient writers? It seems to me that by comparison, it was only a very few who had the means, either through individual wealth, or the backing of a church or government, to get widely published and to get notoriety. It is possible that was a reason that infant baptism didn't have widely published opponents. It was popular, so the only ones who got the ink were on message.
Councils are to verify what is the true teaching in the face of contradictory teachings.
That sounds exactly like what our Supreme Court does. When different Circuit Courts disagree as to interpretation of a statute or the Constitution, then the SCOTUS verifies the true meaning. Both declare what is the interpretation of the governing document (Constitution or Bible). The only difference is that the SCOTUS is specifically ordained in the Constitution. I don't know where Councils are to be found in the Bible.