Such genealogies were popular in the late medieval period among the merchant class and minor nobles, with something of a Victorian era revival of the practice, it lent a little grandeur to those striving for such. Think Millicent Bucket, lol.
The one I saw did follow the legendary path to the letter, but included an individual belonging to a no doubt mythical people of Ireland, the Tuatha Dé Danann, so it's apocryphal.