“A canon of a council is not ipso facto a dogma, but conciliar canons can contain and define dogma.”
That’s a standard face-saving device which Catholic apologists use to immunize their church’s infallibilist claims from falsification. However, they pay a price.
When a teacher hands out an exam, he has a test answer key to grade the exam. The answer key has all the right answers.
However, Bryan is treating the text of an ecumenical council like an answer key with some wrong answers (who knows how many?). So he's trying to grade the exam using an errant answer key. How can you correct an exam using an answer key with incorrect answers?
You'd first need to know which answers on the answer key are correct and incorrect before you could use the answer key to correct the exam. So what are you using to correct the answer key before you use the answer key to correct the exam?
So this poses a dilemma:
i) Either we already know where the true lies before the council speaks. In that event, the council is superfluous.
ii) Or else we’re dependent on conciliar statements which are, by turns, true or false. In that event, we’re in no position to winnow the true statements from the false ones.
If the text of an ecumenical council contains both true and false statements, then you can't use an ecumenical council to winnow truth from error. Rather, you need some winnowing fan independent of the ecumenical council to thresh its true statements from its false statements. But if you’re dependent on the ecumenical council, then you’re lost in the jungle.
The Catholic rule of faith always devolves into a vicious infinite regress.