He is a fantastic sermon of Fr. Pfeiffer in 2005 speaking of God's order. In it, he also spoke it is better to have a bad father than no father at all...and, when there is no pope (intern) between the death of one pope waiting for another, there cannot be any plenary indulgences. Because one of the conditions is to pray for the pope.
A practical consequence for sedevacantists who say they have no pope, it results, they have no plenary indulgences. Further, they have no culture to pray for a pope (when peter is locked in chains), no culture or guide to raise their children, no order to place their identity.