Heard from one person who was confused about the results, so let me make this clear. What we can conclude from this is that:
A. So far, and at least to my satisfaction, the Vliet surname and Flatt surname are not related, thus the Spotted Cow story is a myth disproven by DNA. (See the "Debunking" post farther down this page). I still want to collect some more Vliet and related surnames samples, such as from Adrian Van Vleet descendants and some Van Fleets of Dutch origin in order to round out that surname, but cannot find any DNA nor paper evidence, other than circumstantial, that the Vliet surname turned into Flatt at some point.
B. Have one Flett DNA sample which not only is in the same haplogroup, but matches fairly well on a large number of markers. Not a perfect match but much more in the range than Vliet; and the origins are Orkney Islands, Scotland. The researcher doing that testing plans to add a lot more samples as time goes on and his purse permits, so over time we should have even more samples to compare with (Note: If anyone knows of a Flatt in Scotland or Ireland that would be up to take the test, tell him to contact me)
C. Although the Flatts in PA/NJ/TN/KY/MD etc match very well, it does not follow that they are matches within one generation. In fact, as noted in other comments I have made, there are some serious logical flaws with attempting to fit all the Flatts into the James Flatt m Elizabeth Dupree model, not the least of which that one other line, the John Flatt m Mary Savage line, has a tradition of coming over to the Washington DC (Maryland) area from Scotland in a later time frame than James Flatt was in New Jersey. And, of course, we know there are other instances of Flatts coming to America at various times, including, for example, the indentured James Flatt that went to the Carolinas, or the (presumed) widow, Ann Beaton of a Flatt-she went to Concord, NH. (I conjecture he was a James Flatt as well since Ann's daughter named one of her sons James Flatt Melvin). What I'm saying is that we have many strings from various family lines that do not, at this point, lead up to a common ancestor, although they very well might. Nor do I think that it's a necessity that they have a common ancestor.
It is entirely possible, and in fact, probable, that the Flatts some generations back came from a common point in the world, but came to the US at different times and were not necessarily closely related, as in brother and sister, etc. We just do not know. If, for example, everyone that tested was a close match on 37 markers, then 50 % of the time there is a match within 5 generations, but that's also 50 % of the time there is not. In other words, the DNA test has to work to some degree along with a paper trail in order to get more granular on family relationships.
As I mentioned when I first started this project, one main goal was to prove or disprove the Vliet/Flatt theory. And again, although I intend to get more samples (and should I find, amazingly, a match, I will reverse myself), at this point I am satisfied that anyone who is of the Flatt line from TN/KY/PA/TN that is not of German or Slavic origin should correct their records and leave off the Vliet origin.