David, please excuse me, but this doesn’t appear to make sense. What’s the point of an infallible magisterium if 1. it almost never exercises its infallibility, 2. if it almost never defines what’s explicitly infallible, 3. if it can’t even be sure of itself until after the fact?
I am sorry to use such strong words, but: a lot of this sounds like the rationalizations of a Church that does not know what it’s talking about: “Oh, X is probably infallible but we can’t know it until the infallible hierarchy infallibly defines what infallibility is, and then we can’t be sure if the infallible definition of infallibility is infallible because it might actually be fallible until we are infallibly told that the concept of Infallibility is infallible”, etc.
If only the Magisterium would properly define itself as clearly as it does almost everything else (Transubstantiation, the Assumption, etc.) ! All the official definitions of authority in this matter are confusing and roundabout. For example, Bishops speak infallibly when, across the whole world, they proclaim a single doctrine with one voice in union with the Pope - yet this almost never
actually happens! It’s simply theoretical.
What’s the point of hypothetical infallibility when we can’t ourselves discern between Official Church Teaching vs. One Pope’s Opinion?

It seems to get right down to the same issue as Sola Scriptura.