My cousins researched our lineage "Claypool/Leonard".They are dead now so I can't verify where they obtained the information on the Royal Houses but they researched and traveled for 19+ years.We have found only two errors in the book dealing with our individual lines.
FYI: This is part of the lineage of the Claypools.
Goeffrey Fitz-Piers, Earl of Essex and Lord High Justice of England. Lady Maud, m. Henry de Bohun, a Magna Charta Surety, who died in 1220. Humphrey de Bohun, Earl of Hereford and Essex, d. 1274; m. Lady Maud, daughter of Henry, Baron de Eve. Hunphrey de Bohun, Govenor of Goodrich and Windsor Castles, m. Lady Eleanor de Braose, daughter of William de Braose of Brecknock. Humphrey de Bohun,d. 1297; m Maud de Fines. Humphrey de Bohun, Earl of Hereford and Essex, m. Nov. 14, 1302, Princess Elizabeth Plantagenet, daughter of Edward I of England. William de Bohun, d. 1360, created Earl of Northampton in 1337; m. Lady Elizabeth Bartholomen de Badlesmere, daughter of Bartholomen de Badlesmere who was executed in 1322. Lady Elizabeth de Bohun, m. Richard Fitz-Alan the tenth Earl of Arundel. This is where the de Bohun name ended in our line.
I believe the library can give you the information on how to obtain documentation on the lineage of the Royal Houses.
I hope this is useful to you. Happy Hunting Dorothea