Except for some Royalty and even then such is questionable, there is no paper trail from Roman Times up to the Norman Conquest, and even that which follows is as much fabrication and myth as fact.
But the Celts, of which the Icene tribe was one had no written language hence no documentation, and except for scant Roman accounts, many of which are themselves questionable, there were no records until Saxon monks started keeping records, and again, those records are in much dispute, today amongst scholars.
And that brings up the sore subject of documenation. There were no such things as marriage licenses, birth certificates, death certifcates until the mid 18th century (Marriage licenses in Virginia appeared), they slowly caught on, because of legal (inheritance issues), birth and death certificates didn't appear until the 20th Century, and even then many at home births were, and even today, are not recorded.
My grandfather was born in 1883 and had to register for the Draft for WWII, but had no birth certicate. He had to travel to the county seat with a relative who testified for a Delayed Birth Certificate.
The Catholic Church and subsequently the Anglican/Episcopal church required the issuance of Banns before the priest could officiate at a marriage, and all too often the parish registers were lost when the church was disestablished, or lost to the ravages of war, fire or flood, or even a departing priest (or pastor of a small protestant church) moved on and took his notebook with him.
This was the fate of the notebook of Rev Wm Douglas of St James Northam Parish, Goochland VA. He pastored three churches in St James Northam parish, and each time he took his notebook with him, eventually it was published in the 20th Century as the Douglas Register.
And his was rare event.
Rev Douglas was assigned Dover Church in 1750, but didn't start to keep records of baptisms until 1756. Marriages much later. Thus six years from 1750 t 1756 were lost, those who transcribed and published his notebook as the Douglas Register, dated the marriages of the parents from the date of Christening, which they assumed was the date of birth.
Priest did not keep records of dates of birth, only Christenings, so the published dates of births in the "register" are in reality the dates of Christenings.
If I recall correctly, and I may not, it was the custom, in days of old, for the Catholic religion to require that an infant prove viable before it was Christened, and at one time this meant a year. If an infant died before it was Christened it was believed to be unensouled and it would lie in limbo.
The point is that there is little to no documentation of birth prior to the 20th Century, and such that exists is deduced from wills, Family Bibles, and church registries.
And Family Bibles are problematic, because the Bible usually winds up in the hands of the oldest daughter, who marries and changes her name, and it eventually winds up, if it survives that long, in the hands of a family for whom the original family is unknown or of no concern.
Most family bibles are recreations (from memory which is often faulty).
Very seldom was even the oldest son in the family, even interested in a family bible, he had more important things to attend to, like earning a living and feeding his own family.
The mother was generally the family historian, amongst other things.
Much family history was passed down verbally, and in the process it gets altered as we all who have played "telephone" know.
I have personal experience, being raised in backwoods southern Arkansas in the 1940's ,, sans electricity and plumbing.