Mmm-don't know, Carol, but these families are certainly all in the right location--Prince Edward created from Amelia 1754, Nottoway from Amelia 1789.
As best I can determine, there were only two VA McClurg families--and it's quite possible your Nathaniel and my James were related since they're clearly in the same general area--though James was probably older, born about 1765 based on census ranges and married before 1796 or so. He was on the 1791 tax rolls in Nottoway.
I have not researched Samuel Morgan--though I gather there were several Morgan families in Nottoway. My plan was to try to find him in Amelia earlier.
It may be that we're looking at members of the same family, but since I haven't done the VA research yet, hard to tell how they might be related!