Sources

1) Source: Court of Chancery: Six Clerks Office: Early Proceedings, Richard II to Philip and Mary "Plaintiffs: Richard Beauchamp, esq., son of John lord Beauchamp, and Elizabeth his wife, daughter of Humphrey Stafford, knt., late of Grafton.". Reference: C 1/24/186 (Data from direct source)
2) Source: The visitation of Yorkshire in the years 1563 and 1564. Reference: 63-66: Constable of Flamborough (Questionable reliability of evidence)
3) Source: The visitation of Yorkshire, made in the years 1584/5 Constable of Flamborough, Everingham. Reference: Pages 197-198 (Questionable reliability of evidence)
4) Source: Court of Chancery: Six Clerks Office: Early Proceedings, Richard II to Philip and Mary "Plaintiffs: Thomas Chaworth, knt. and Isabel his wife, and Eleanor, late the wife of Humphrey Stafford, knt. of Grafton, daughters of Thomas Aylesbury, knt., descendant and heir of Hawise Kaynes." Hawise de Keynes was Eleanor's Great-Great-Great Grandfather.Dated: 1454. External Link
http://discovery.nationalarchives.gov.uk/details/r/C7441321. Reference: C 1/24/51 (Data from secondary evidence)
5) Source: Privy Seal Office: Signet and other Warrants for the Privy Seal, Series I "Humfrey Stafford of Grafton, husband of Eleanor, daughter and co-heir of Thomas Aylesbury for dower of Katherine, his widow"1439. Reference: PSO 1/63/14 (Data from secondary evidence)