In Catholic thought, bishops are the successors of the apostles, with the laying on of hands from bishop to bishop all the way back to Peter.
Some Anglican and PNC bishops have valid apostolic succession according to Catholic standards, though their ordination is not licit, or something like that. Not all, but some. However, I want to look at the possibility that some Catholic bishops are not in the succession due deficient ordination or other defects. There are certain conditions under which apostolic succession is invalid, such as lack of intent. The thought crosses my mind that one cannot know whether one’s own bishop is validly in the order of apostolic succession. He may claim it, but can he prove it?
In the Middle Ages and earlier there were times when almost all the bishops were corrupt or ineffectual. Bishops were installed to consolidate political power, to obtain money, to be manipulated - in short, for all the wrong reasons. Not everywhere, not all the time, but it was prevalent. So they were not really bishops, so the priests they ordained were not really priests, so the Eucharist they attempted to consecrate was not really transubstantiated.
So when a Catholic approaches the Eucharist, he assumes that it has been validly confected by a valid priest. For what reason do you proceed on the basis that your priest is validly ordained? What if you discover his ordaining bishop wasn’t validly ordained? Or there was a break in 1402 or some such year? Does this happen? Is it of concern?