Let’s look at it this way. What the apostles wrote down, we know there was no mistake. Why? Because they walked with God, who was God in the flesh, right?
But the Popes of centuries later have not. They were all elected religious officials. Most were elected by cardinals or somebody like that. Now just how does a Pope during a certain century come up with a new ex cathedra decree? Well. he would consult the teaching order of the church on a teaching. Then he see how the Catholic people thought about it in general and then decide just what he felt about it himself.
This is pretty much how two Popes decreed the ex cathedra doctrines of the immaculate conception and the assumption. They saw that the church throughout the centuries highly regarded Mary as sinless and their were some writings of her be assumed to heaven. The Popes read where certain writers in church history felt Mary was sinless. The Popes then decided to make it an actual teaching for all time, based on this methodology.
I can understand that. But what happens when some future Pope declares something that never was written about in history or the Catholic people never pushed for anyway? Will what he decrees, still have to be accepted? Like I last posted, where he might decree Mary as a co redeemer, along with Jesus, where she can forgive sins, just as God? What then? That was my point. Are Popes infallible irregardless? I don’t believe so.