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The assumptions and statements you made in both of your messages were unclear as to your specific meaning, if not outright erroneous.
As I clearly stated on my Web site in the section "Who Was David Porterfield, Sr?" and the subsections "Who Were His Parents?" and "Who Were His Grandparents?", my undocumented THEORY is that the James Porterfield who married Catherine Maxwell was the the son of Robert Porterfield (1716-1785) and the grandson of John Porterfield (1675-1739) of Donegal County, Ireland. This is the theory I will stick with until I or someone else proves differently.
The only James Porterfield (1718-1777) who was the SON of John (1675-1739) of Donegal was the James who migrated to Cumberland County, NC and died there in 1777. As existing documentation clearly shows, James (1718-1777) of Cumberland County, NC very definitely was NOT the James who married Catherine Maxwell. The Cumberland County, NC branch of the Porterfield tree would only have been cousins to David Porterfield, Sr., since James (1718-1777) of Cumberland Co., NC and Robert (1716-1785) of Lancaster Co., PA were brothers.