I’ve got a whole bunch of mystery lines, genealogically speaking, on both maternal and paternal sides, that I can only find record of to the early 1500’s in modern-day France, German speaking and near the Rhine though, in Alsace, with a few in Canton Basel, Switzerland, and a few on the other side of the Rhine. All their surnames could be considered Jewish, but they were Moravian. Had a penchant for Hebrew placenames in PA and NC. Bethlehem, Bethabara, Bethania, Salem. I’ve often wondered who they really were, and where they came from. Spain? The era is about right, for them to just pop up like they seem to have.
Yeah, I used to do a bit of that sort of thing and came to the conclusion that it wasn't a terribly good idea. Unless there's a reason to track genetic diseases (or if you're Mormon), noodling around in who really begat who can be rather eye opening, pointless, and impossible all at the same time.
I found I really didn't want to know some of the stuff I discovered. Coming to the conclusion I was committing genealogical voyeurism, I've adopted the Popeye philosophy on researching the family tree, “I yam what I yam, and that's all that I yam.” It works lots better for me.