My parish in my hometown has records of my baptism and confirmation and first communion, and it is reasonable to believe the ancients were as meticulous about their records as we are today, even if they didn't have FileMaker Pro.
Why would you consider that a reasonable assumption for the whole of Church history?
There have been plenty of events that have disrupted regular parish goings-on, and there have been plenty of incidents through history where entire parish churches or their records were destroyed by war or sectarian turmoil.
And in the old days there was nothing but the Catholic Church, and people didn't move around much, so it would have been very unlikely that a person was not baptized but told he was, and there would be no reason for the parents to lie about something like that. Their own immortal souls would be in peril.
That's only one example; my point was that it's concievable that under the rules and laws of the Catholic Church, it's possible for even a genuine, honest man to go through the rituals and not be a valid bishop. On top of this, there is the possibility of genuine deception:
When we look at the last two thousand years of Christian history, we can see that "people who didn't move around too much" spread Christianity outward from Rome, and then:
- moved from Roman Britain into Pagan Ireland
- moved from France into Britain with the Norman conquest
- moved all over Europe to avoid successive plagues
- moved all over Europe to avoid successive wars
- explored the world and colonized vast swaths of it
- spread missionaries all over the planet
There are plenty of times throughout the last 2000 years of history where it was far from a simple matter for a representative of the Church to confirm details about a candidate for bishophood.
Put yourself in the position of, say,
Bishop of Quebec Francois de Laval circa 1670. A "priest" comes before you bearing letters from Rome (genuine, but stolen - he killed a priest travelling to the port in France and decided to take his place on the ship to the New World) instructing you to place him in a parish church. It would take a year or more to get a message to Rome to ask for confirmation, and any response would appear to confirm the interloper - after all, he fits the general description of the right man, and there was no photo ID in the 17th century.
As the Church in the New World expands, what would happen if that "priest" was elevated to bishop of his own diocese?
With countless possibilities of events like this throughout the last two thousand years of history, how can it be reasonable to assume that the events resolved themselves in favour of Apostolic Succession
every single time so that
every single bishop in the Catholic Church today is valid?