I didn’t say, or at least I didn’t mean to say, that the Popes have taught infallibly only three times. The Pope, the bishops, all priests, and all Catholics, in fact, teach and believe infallibly when they teach and believe what the Church has always taught and always believed.
I’m not talking about niggling controversies or messy situations (such as when the state has interfered with the Church’s freedom to govern or teach), but the main outline—the Apostles’ Creed, the Nicene Creed, the Councils, etc.
That changes subtly here and there...with early words which were used redefined to include the latest development -- when the contrariness of this or that thing is not simple denied, or explained away in gushing torrents of "explanation".
The main outline, going that far back?
You've got to be kidding.
The bishop of Rome settled none of those things.
In those days none looked to that bishop as those of Rome in later centuries came to.
The only reason his signature or agreement would have been necessary is that without it -- there would have a significantly large portion of the Church under a single bishop (that would be the one in Rome) in disagreement with either all or a majority the rest.
That type of disunity was sought very much to be avoided -- but Rome was sitting in the driver's seat of none of the earliest Councils.
Go back far enough, when one of the first times a bishop of Rome attempted to throw his weight around and command others to obey, or else be excommunicated --- the majority of the bishops quite directly reproved him for it, even as a majority, chiefly in Western realms agreed with that which he had tried to first ram through on his own claim of "authority" (with the setting of date that the Resurrection was to be observed upon).
In later Council -- the bishop of Rome was again reproved but more gently --- basically told to go back to the way things were before and him not try and appoint bishops not under his own 'patriarchate' (in other words -- get his big fat Roman nose back on his own side of the Mediterranean!)-- which was also the first Council to put that patriarchate idea in writing, that idea too being a thing of development in the wider Church.
All along the way there are signposts and markers along the road to the hyper-inflated claims of "authority" which we are talking about even at this very moment!
mary mary, how does your garden grow?