And I thank you for your excellent citation regarding the age of the James Abernathy who married Elizabeth Cox. But I still doubt a James being identified _in_ the will signed on 31 Jan 1772 by the individual we identify as Robert 3rd although he did sign as a witness. Nor do I find him _in_ the will probated after 1779 belonging to the individual we identify as Robert 4th, save as witness. I have transcriptions of both of those on my website and the only place that a James Abernathy appears is as a witness. Deduction of his relation to the signer of that will is not indicated on my copy of that will, merely that he signed it as a witness (signed with mark on the earlier one, with his name on the later one). Transcription of the 4th Robert's will supplied by John E. Abernathy Jr (of the Giles County TN Abernathy branch) thusly [Raleigh Loose Papers, CR060,801.1, Robert Abernathy: Binder note says "No date, probated 1772 (1772 crossed out) probated after 1779)and that the will was hand-written. A local NC researcher has stated that probate was in 1792, presumably before the original papers were transferred to the Archives in Raleigh, NC.]
As for the researches of Birdie Abernathy Mrs Alfred Jamison, I have her documented as born in Quitman, Clarke County, MS in May 1889 and died in Nov 1989 in Batesville, Panola County MS. Her notes give her marriage in 1908 but I am not sure they tell where. However in 1900 she was listed on the Adair County, MO census. There is nothing to indicate in those notes that she ever even visited NC. Her husband and her father were both doctors, and she is of the lineage that descends from the James Abernathy who married Elizabeth Cox. But her branch that left NC between 1820 and 1830 to migrate via AL into MS before 1850.
Finally, as for the maiden name of the wife of the 2nd Robert, Margaret Ogilvie's research a few years ago determined that Christian was a Parham prior to her marriage due to the 5 Apr 1712 survey of a 100 acre platt of land that is described in the Prince George County, VA's Surveyor's Platt Book, p. 6, as "100 acre platt of Thomas Parrum's [sic] land alias Robert Abernathy's land." which evidently was Christian's dower land from her father, presumably the Thomas Parham who sat on a coroner's jury in Charles City County VA as of May 1665 along with the 1st Robert Abernathy. Source: Charles City County Court Order Book, 1655-1762, on microfilm from the LDS Library Catalog, Call #30989.
We have not a single iota of documentation to attest to the birth year of the 2nd Robert, merely an inference that he was probably born abt 1660 and died after 2 May 1727. Solid documentation regarding the birth year of the 3rd Robert is likewise somewhat missing, but was probably between 1682-1699 and his death was shortly after 31 Jan 1722, which is a rather long lifespan for an active male of that period.
Birdie mentions the 3rd, 4th, and 5th Roberts in her 1953 'genealogical data' (donated to Marguarette Wms. of Sanders, Senatobia, MA, source: LDS microfilm call # 1035838, item 13). As I have stated, Birdie does not tie specific actual facts directly to any specific references, which is a pity, but they were clearly notes, not a formal paper like unto a doctoral dissertation.However, for the 3rd Robert we do have Brunswick and Prince George county, VA Deed dates from 1712 to 1739 that we can document and attribute to that Robert and probably no other Robert Abernathy.