I've found another Robert Duke! But first, some background.
A huge problem for anyone who studies genealogy is the fondness that our ancestors had for reusing names. Another is the persistence of bad information. I encountered both early in my studies. My 6-great grandfather Richard Burge is a good example. In the 1700s, three generations of Richard Burge were born, but not in a direct line as many, including me, first assumed. After a year or so of digging into the scant historical records, I realized my mistake. My ancestor Richard Burge was the son of John Burge, who happened to be the elder brother of a Richard Burge. It took another two or three years to convince other family researchers of that truth and even today, over a decade later, I still encounter web pages that perpetuate the mistake. It's particularly annoying to me to find that the mistaken information are old data copied word-for-word-without-credit from my early work. I suppose I should be glad now that my name isn't attached to the error.
I found the similar problems with my Duke line. In 1990s, a book was published that discussed a singular Robert Duke who had a son named Moses. The two lived and died in South Carolina, with Moses Duke dying in 1821, according to the book. I took exception to the book because my 4-great grandfather Moses Duke from that area of South Carolina was alive in 1840 and living in Alabama. After studying the historical records for the area, I determined that there were actually three Moses Dukes and five Robert Dukes during that time. My study can be found in my Dukes of Camden District, SC note, which is still a work-in-progress, by the way. And yes, despite the passage of half a dozen years since I proved the finding, I still have to convince other genealogists.
Now back to Robert Duke. I've found a sixth one hidden among the others in the old Camden District. Actually, there is a seventh one, too, but that's another story.