I think I may have answered my own question. Today, through the National Archives, I accessed online the pension application of the Pulaski County John Newby. By his declaration he served from April 1777 until August 1880 in eastern Virginia, North Carolina and South Carolina. There is no evidence that he was in Kentucky in 1779.
I remain curious as to why John Newby isn't on French Tipton's list of Madison Countians at Boonesborough.