I have no idea. But I'm not concerned about it, because I don't think as a sedevacantist does.
I understand that everything has to make perfect sense to a sedevacantist, but as +ABL said many times, there is a certain mystery to the Crisis that we cannot understand. "It's a mystery!" he used to say. He was right, IMO.
Well, if you could explain it to me perhaps I would stop being a sedevacantist and join you.
I only care about the truth and not "what side" I'm on.
Once we "take sides" we only look for information that fits our confirmation bias.
Perhaps I am wrong about sedevacantism.
Perhaps ABL is correct and these popes were antichrists but they were not heretics because if they were heretics it would mean their elections were invalid and apparently that simply cannot be.
Maybe somebody else here has the answer.
Is it truly possible to be an antichrist and not a heretic?