It's been a few years since this post, but here goes. My husband, too, is directly descended from William Douglas and Sarah Proctor of Connecticut. I think your guess is a good one - or that the Sarah Proctor who married William Douglas was entering upon her 2nd marriage, the first one to a Proctor and maybe she was a widow? I can't find any other information either, and the multitude of people jumping on the Proctor/Basset parentage has led to more confusion. Have you been able to learn anything more?
Thanks for stating the facts so plainly and completely.
Laura Hunnicutt Gardner, Indiana