Thanks to both :) I second the implied motion that it would not be the best use of my time to try to sort out the American genealogy and find Sally's real parents, especially as I have no expertise whatever in those records.
If no rationale is forthcoming to make a connection seem plausible, I think I will just quietly snip the link.
I've looked at the Bideford side and think it more likely that William is the William Skriggins who wrote a will in Merton (11 miles away) in 1801 and died there rather than that he emigrated to the US. If that's the case, he would have been only about 19. Unfortunately, I think it one of the wills lost in the Exeter bombings during WWII, so no light there.