It is a shame that I am just now getting into using the Message Boards and have found this post. I hope you are still out there.
I think your info may relate to my line, but way above where I have been able to get.
My g-g-grandfather and other siblings moved from Bradley County, TN to Texas in the late 1800s. My g-g-g-grandfather and some of the other children stayed in TN.
My g-g-g-grandfather is the David Cowan listed in the 1850 Bradley County census with wife Elizabeth (Sarah Trewitt). I haven't been able to confirm a connect to his father which is possibly one of the Andrews, Johns, or James' there or in nearby counties.
Since they usually named their first born after the grandfather, it is likely that Samuel's son David that you listed is up the line from mine.
I am very interested in hopefully closing the gap between the two with any information you might have.