When shared information doesn't add up, Part 2

So up to this point, I'd been relaying the background on a Williamson family that I have been tracking in Parke County, Indiana. New evidence seems to be pointing to Greene County, Tennessee as their place of origin, or at least, where they lived before moving on to Indiana. To begin my search there, I started looking at the Ancestry.com message boards looking for others who may have already dug up some useful info on Williamsons who may have been living there at the same time as Clement. All of his known children claimed Tennessee as their birthplaces and this group goes back to 1817 so I knew that I should be able to track them there at least that far, and thanks to familysearch.org, I was able to locate an exact marriage date for his presumed daughter, Elizabeth Williamson, and her husband, George Basinger, who were both mentioned in Clement's probate file in Parke County as heirs. With all of the information I collected, it set up an estimated birth date for Clement between 1780 and 1790. I didn't find anyone of that name mentioned in the Greene County, TN message board, however, there was another Williamson found of a comparable age. Thomas Williamson married a woman named Kezziah in Greene County and had several children. More importantly, he left a will which named several heirs. There were quite a few posts from people claiming to be descended from Thomas and considering the closeness in age, I thought that perhaps he could be a cousin or brother. So my first question to the message board was if anyone had done any work on Thomas' extended family, including siblings. I didn't get an answer to that, but I did get a response from someone who had some information to share, though none of it was sourced. What she told me points a big fat red flag at the current state of Williamson genealogy.

It appears that Thomas Williamson named a daughter in his 1836 will named Elizabeth. More importantly, Thomas' descendants are attributing that 1831 marriage between Elizabeth Williamson and George Basinger to the daughter of Thomas, not the daughter of Clement who they may or may not have known about in the first place. Now this creates a problem because either there were at least 2 Elizabeth Williamson's living in Greene Co, one a daughter of Thomas and one a daughter of Clement, or there was just one, the daughter of Thomas and upon his death, Clement adopted her or at least took her into his own family and from there, they left for Indiana where they continued to live in close proximity to one another.

So which one is it? Were there 1 or 2 Elizabeth Williamson's? And if there were two, which is which?