The magisterium

I am kind of confused about something.

So the magisterium was created through vatican 1.

So if the magisterium only exists since vatican 1 then that means that all papal teachings post schism and pre vatican 1 can be fallible ,since they have no magisterial weight,and can therefore be not accepted if someone where to choose to do so.

And if papal infallibility was already understood as defined in vatican 1 then why did certain groups disagree with this teaching,forming the Old catholic church?