I challenge your statement in the above message to the effect that the 20 yr old James Abernathy was a son of the 3rd Robert Abernathy. The lifespan of said James Abernathy was from 1743 to 1785 (when he drowned about aged 42) but the will of the 3rd Robert was signed in Jan 1772 while said James was still alive and he is emphatically NOT mentioned in the will of the 3rd Robert!
I thank you for your pinpointing his birth year, because it has caused me to move him from potential grandson or great-grandson of the 1st Robert to yet one or two more generations removed. This is the 2nd date adjustment that I've made to my database in the past month for the earlier members of this particular line: I am still not sure that I accept the birthyear of abt 1682 for the 3rd Robert from Birdie Abernathy Jamison's 1953 Abernathy-Abernethy genealogical data typescript collection because she did NOT include a single proper cite so that we who follow behind her could verify that her 'facts' are accurate. If her dates are correct, then the 3rd Robert lived for 90 yrs, +/- and that's an awfully long time for the men to live during that period of our history.
But I am reasonably sure that James is NOT a son of the 3rd Robert, nor the 4th, nor even the the Robert. The 4th Robert's will was probated in 1792 if my information from a local descendant is correct, and he is not mentioned in either the wills of the 3rd nor the 4th Robert. You see, James Abernathy witnessed the will of the 4th Robert Abernathy and there is no mention of him in the will of either will at all!