You asked "Is this the same Robert you have listed as an indentured servant who could not write?".
Yes, it is.
I cannot help that you find it 'odd' that Robert & Sarah would be among the unlearned because there _IS_ an official document to demonstrate otherwise: in the records of Charles City County, Court Orders, 1655-1658, p. 98, where the microfilm image clearly shows that neither Robert nor Sarah could sign their own names. And that realization was, for me, the final nail in the coffin of Robert's alleged descent from an aristocratic Baronal Scottish family!
I descend from the third son of the third Robert but I do not descend from the English Tilghman or Devonshire families and neither do you nor anyone else who descends from the individual you and many others persist in erroneously calling Robert A. Abernethy (or Abernathy).
And that is because Christian Abernethy, wife of the 2nd Robert was not who you assume she was. The small plot of land transfered to the 2nd Robert as part of his wife's inheritance from the 1717 will of Susannah Tillman had previously been in the possession of her 1st husband (a Parham) and not a Tilghman. As I believe I have posted in this very forum about 4 years ago [msg #2735].
Just as I have affirmed the conditions which caused those who believe that the first few Roberts all had a middle initial of 'A' when that was, in fact, a short-hand method of indicating the full surname in order to conserve space and cram more information into a limited space newspaper column back in the 1930's and is not found in ANY official document relating to the individuals as published prior to that year. Certainly none of the official documents produced during the lifetimes of that individual ever identify him with such. And darned few of his male descendents had a middle name until a good hundred years or more after his death.
If you wish to believe in beguiling myths, that's your look-out, but please don't try to use your obvious myths to call into question facts given with specific cites for any and all to verify when those facts run counter to your myths.
A reputable genealogist, professional or layman, must ALWAYS be willing to throw out that which can be demonstrated with historical evidence to be unfounded.