I think theologically the priests and laity on all three "sides" got a pass on that issue, since the three claimants unlike today, believed, thought and spoke as true Catholics. Today it is very cut and dry to know who is not a True Vicar of Christ. Unless one is obstinately deluding himself. But back in the 1300's the Faith was very strong and it was infinitely more difficult than it is right now to discern who was the True Pontiff. The fact is except for the anti-popes, no cleric and/or faithful was excommunicated for erroneously believing any of the three claimants at the time was the legitimate Vicar of Christ on earth. St. Vincent Ferrer comes to mind.
Like I said, Today, the situation is crystal clear.
The situation is not crystal clear for thousands of devout little old ladies and a few old men who continue to gather together for the Rosary and are persecuted by certain priests for doing so. Pushed out of their local parish churches, they gather together at local cloistered monasteries where the nuns welcome them.
They go along with the Vatican II New Church because they were raised Catholics and believe everything that comes from the mouths of their priests and Francis. They believe that they should not judge nor gossip.
If anyone were to try to convert these old ones over to Catholic Traditionalism, these gray panthers would shake their old bony fingers and attack with the mantras instilled by Vatican II: Do not judge; do not try to be holier than the pope; and finally, do not be part of the problem, instead try to be part of the solution and pray.
What can we do? If anyone were to try to convert these ancient ones to Traditionalism, these ladies and gentlemen might lose their faith all together. They are so naive, and yes, gullible, but they remain firm in their belief that the pope can do no wrong, and that the gates of hell will not prevail.