Ancestors of Jael Duncan Stallard

It has been believed, based on information published in the book "Stallard Connection" 1981, that Jael Duncan Stallard, the wife of Samuel Stallard, had the following ancestery going back to Rev. William Duncan of Scotland.

Although Rev. William Duncan is a well documented and no doubt colorful figure, recent research by the genealogist Dr. John A. Robertson of Scotland has cast serious doubt as to whether the reverend's descendents ever immigrated to Virginia. Thus, the ancestors of Jael Duncan should be carefully re-established.

Nancy Reba Roy, in her monograph entitled "Descendants of William Duncan, The Elder" published in 1959, describes the descendants of William Duncan born in 1692 down to Jael's marrage with Samuel Stallard. Some doubt can be cast on the validity of her research because 1) she claims that William the Elder is the grandson of Rev. William Duncan of Scotland and 2) she makes the unfounded claim that Walter Stallard immigrated from England and settled in Rappahannock Co. VA in 1640. For the time being, we can only assume that Jael's grandfather was indeed William the Elder, but unfortunately we can't go farther back. Can anyone trace William the Elder farther back?