Diana, I am not a Duty researcher but was just in contact with one and did a lookup in some books I have at home for Fauquier Co., VA, where there is a 1761 deed for William/Caty Duty of Prov. of North Carolina who I thought might be your's.
I see your line is Thomas Duty and Martha Roman of VA. This fellow is looking for Thomas and Pretious Duty with a son Daniel and possibly sons John and William (at least those names mentioned in an estate settlement in 1807 Loudoun Co., VA). Pretious is possibly a Jewell (no pun) and that's where I come into the picture. There's also a 1794 appraisal for Charity Duty.
Have you come across any of these names before since Loudoun borders Fauquier?