The "Millenium File" is compiled by a purported research firm of unknown character from 'client records' and other sources of an unknown nature.
There is no way to know whether any historical records at all were used to compile it. If Great-Aunt Hattie wrote up something for a 1923 Family Reunion, and said she thought her father was a descendant of XX of Revolutionary War fame, who she thought was a descendant of Charlemagne, that could be a 'client record' used in this compilation.
Consider it to be genealojunk and don't waste your time with it. Many books include hoked-up royal lineages; any of these could have been sources for this material. Or not. There is no way to tell.