I do not know if the Catholic Church has "an official position" on the length of Peter's bishopric in Rome, or on the starting and ending years of his bishopric. My hunch is that the Church leans on historical scholarship to determine those dates accurately. What is important for the Church is that he was at Rome and that he was martyred there.
-A8
Other than Eusebius and Jerome, and they were late, in the 4th century, I have found no other early church patriarchs that give credence to Peter's Bishopric.
I checked Clement of Rome, Ignatius, Justin Martur, all of whom were early enough and connected enough to Rome to know the facts. If anyone would attest to his Bishopric, they would, but there is nothing in their writings. Surely Peter's Bishopric in Rome would show up in their writings if he had been there, right?
The earliest attestation that Peter was even in Rome was Irenaeus whose only attestation is of the "Church founded and organized at Rome by the two most glorious Apostles, Peter and Paul". That's all. There is no mention of a 25 year bishopric, Nero, dates, crucifixion, or death of Peter in Rome.
Where did Irenaeus get his information that Peter had been in Rome with Paul establishing the Church there if it is not in Scripture or in any of the patriarchal writings before him? Did he just make it up or did he read about in the Gnostic Clementine literature that was going around which was hardly credible?
What credible patriarchs of the early Church am I missing?