Two earlier threads on RCC hierarchy and titles:
Knowing that my wife used to use the nick Evaine II may clue you in to how we feel about the Deryni series. 
As you may note from the maps, the Eleven Kingdoms, which are mostly later united into Gwynedd, are effectively the British Isles in a world where the Irish Sea and most of the North Sea are land. Further, note that the area south of Torenth and R’Kassi is all desert, and under the control of a vaguely “Moorish” group.
Kurtz said in an interview once that religiously her world is a continuation of Catholic Christianity of the later Dark Ages, when national churches vaguely unified were the seat of power, and the Papacy was at its low ebb. Now imagine that situation with Rome having either become an abandoned city in the desert or under the control of the Moors, continued on to the High Middle Ages, and you have a handle on Deryni-times religious polity.
The itinerant bishops, by the way, are not invented – this was a feature of the Celtic church that did not survive the period of intensive Romanization.
Totally off topic-I was baptised by a monseignor (Jacob Shiner).
We used to spend a lot of time with this question with the nuns back in the 1960s when I was in Catholic Grade School.
As I recall, if one should find oneself about to die with an unconfessed, unforgiven mortal sin on one’s soul, one could make an Act of Contrition
An Imperfect Act of Contrition, would spare one being sent to Everlasting Hell, although one would have to do a limited, finite stretch in Purgatory for one’s sins.
or
A Perfect Act of Contrition, would result in one going directly to Heaven