As you are aware, you are the first person to respond to my questions regarding John Porterfield! I am glad to see that someone shares my skepticism.
I do not own the Porterfield book but have access to it at the library.
My primary interest is in the Alexander family. Since Martha Alexander m. William Porterfield quite soon after their arrival here, I am wondering if the families knew each other in Ireland. I also find clues that the Alexanders were from County Donegal. With given names like James, John and William. . . . . I can't be sure that these are all the same people but I am finding clusters of families that they were closely related to in American all in one place in Ireland.
It has been awhile since I've done any of the Alexander research but perhaps we could carry on our 'conversation' by email. Meanwhile, I will look up my notes . . . .