It sounds as though you may be onto something here.William Sale the son of William and Ann (=Nancy) Sale, was born about 1759, so it's not inconceivable that he could have had a son by 1778 (though a bit later would be more likely).I suppose that there's room to push William Erven Sale's birth year back a little bit, and still give him time to get married by 1807.
Very little is known about the William Sale born ca. 1759, as he was in Wilkes Co. NC only sporadically after his father's death.I do not have a list of his children, at least not in my workbook.
Another possibility would be his brother Thomas Sale, who left Wilkes County between 1800 and 1810.I figure Thomas' birth year at about 1755.It had to be before 1761 as his first appearance on the Wilkes Co. tax records is in 1782.
They had a brother Robert and a sister Frances, so the appearance of these names among descendants of William Erven Sale is not surprising if he does connect into our line.
1808 seems awfully early for Obion County, Tennessee, or anything in that vicinity.Thus, I'm wondering whether they might not have made an intermediate sojourn somewhere for a few years before moving to the western edge of the state.