William Jasper Scott birth timing is about the right timing for our Sally Scott that were are looking for. This Sally Scott married Richard Wharton and I think died in Kentucky between 1804 and 1807. He then married Mary Mclellan born 3 Jun 1770 Guilford County.
Robert Mclellan married Vilet Scott cir 1770's and had two children we think James McLellan born 3 April 1772 Guilford . Perhaps this William Jasper Scott is the uncle of Mary Scott we are looking for that raised her after she was orphaned. Though he would be young, back then, responsibility came early in orphan cases.