The link that Bornacatholic provided is to EWTN on the Feeneyites. In that context, knowing the Church to have been divinely established by Christ but refusing to submit to the Roman Pontiff would seem to be intended to apply to Latin Catholics who have been reprimanded by the Church yet obstinately refuse to admit their error.
There's no hint here that this applies to those who are the offspring of centuries of schism and who for whatever reason, simply cannot entertain the possiblity that Roman Catholic claims about the exact nature of Petrine primacy/jurisdiction might be true. The Feeneyites asserted that the Roman Catholic claims are true, indeed, interpreted those claims in the narrowest, most rigorous manner, and, when reprimanded for their incorrect position by Latin Roman Catholic standards view of "extra ecclesiam," refused to submit to the pope's judgment.
Why do you say that this means that I sold you a bill of goods when I explained Unam Sanctam in a non-Feeneyite way?
I don't get it. The body of the Feeneyite decree restates clearly the standard 19thc "invincible ignorance" exception clause for those are out of fellowship with the Bishop of Rome but through no fault of their own do not "know" the truth of the Catholic claims.
Now, of course, some of us on these threads are trying to set forth the truth of these claims. It is possible that the providence of God has brought you into contact with those who assert them in order to give you a new understanding of them. But to do that you would have to have an open mind to entertain their possible truth. Only you and God can tell whether you or I or anyone else has sought honestly and openly after the truth or whether his understanding has been clouded by misinformation or misunderstandings, that is, by the faults of others, including 1st grade teachers, in such a way that you or I are not responsible for not "knowing."
But as in all matters of justice, one cannot be condemned for that which he does not know. The Feeneyites knew--had been put on notice--and they claimed to be loyal, faithful Latin Catholics. That made it much harder for them than those born and raised Protestant or Orthodox to claim "invincible ignorance." They had grown up in the bosom of the Latin Church and were being held to a higher standard.
But in these days, where interaction between the divided groups of Christians, Catholic, Protestant, Orthodox, is perhaps more frequent and more open than in the past where each group interacted primarily with its own members, invincible ignorance might be a much more complex matter.
All I know is that I will have to face God some day and answer for what I was given and how openly, honestly, humbly I responded as I reflected on the truth of the various claims I encountered. I am accountable for how I have listened to or not listened to what Eastern Orthodox say about themselves and about Latin Catholics. I am accountable for how I have listened to or not listened to what Protestants say about themselves and about Catholics. In the end I have to decide which claims are truest, whether and how some apparently contradictory claims might in fact be reconciliable and how some others are not.
It's a bit chastening to realize the seriousness of my obligation to seek truth honestly. We are all scarred by having been lied to, misled, manipulated in the past. We cannot let that make us proudly defensive, only more indefatigable in our desire to consider all claims humbly and honestly.