Exploring the same William Bolen line and have the same problems you have encountered (except for not being a Sullivan but a Bolen). My great grandmother was Anna Bell Bolen that married into the Charles Sylvester Veatch line.
I do have YOUR problem on another family line on my husband. Thought he was a Roberts DNA tested out to be a Mangum/Mangrum from England. Same dead end as you except I do know what line, just not what branch. No unique genes to tell the branch.