Phillip,
My brother has just done the Y-DNA test and we are awaiting results to see where he fits on the Hefner/Heavner etc. DNA Project, part of the World Families Network. I will post the results here. I like your theory that maybe Jacob came from up north to join cousins. I also see in the Johan Dietrich Hafner history that JD and his brother George were two of the first of the German Hefner/Hafners to settle in NC, JD at Howards Creek, Lincoln Co, and George in Catawba County sometime before 1766. Wasn't there just one county then, however? A very nice lady in NC, Freda Reynolds, has offered to help, saying others are looking for Jacob, too (I guess we know that!). She says the latest suspicion is that he descends from George, but she did not say which George and I haven't heard back from her in awhile. In the other matches I'm getting so far they trace to Elizabeth Heavner, daughter of Abraham, son of Johan Diet. Another is Sarah Ann Havner. Some people have her as daughter of Henry Havner and Elizabeth Coon. Henry was son of Frederick, son of Johan Dietrich. Robert and Alfred also had a sister Sara Ann. Do you know if she married a Henline? If you do, this would be very helpful. I do think the DNA may help us figure out this mystery. The confidence level of my match to the person descending from Sarah Ann is extremely high and we are estimated as 3rd Cousins. This causes me to think it is Robert and Albert's sister Sarah Ann, but I need more "proof."