Universal Acceptance is also a bit problematic before the last hundred years or so. I would bet that during most of the Church's history, a good percentage of the Church had no idea who the Pope even was, and would have no actual way to confirm that the man was properly elected. All they knew was that there was some guy sitting there in Rome claiming to be Pope, and they trusted God's providence that this was the guy. 90% of the Church would not have been the wiser had the emperor merely installed one of his cronies in the position.