But the Saint didn't have a problem with people thinking Pope A was real while going to a Mass where the priest thought Pope B was real. This means that those who assist are NOT showing papal reverence to the specifically named pope the priest is mentioning in the canon.
Again, you are missing the critical distinction that those times (Western Schism) what divided them was not issues of doctrine/heresies as it is now between trads and the conciliar church.
The nature of the crisis then was different, those people only had material errors about who was Pope, but among all the potential "Popes" they were all orthodox, not like now when all the post-vatican II claimants are manifest public heretics that push their heresy to all.