Let's put it this way - what the Y-DNA evidence shows is a discontinuity between the tested Woodson descendant and the Jefferson line. It cannot prove *when* the discontinuity occurred - that would require additional documentation that may or may not exist.
The line of descent from Thomas Plummer of Anne Arundel isn't as famous/notorious as the Jefferson/Hemings "connection", but it is considered highly desirable because of a tenuous and somewhat dubious link back to English royalty. The American founder appears to have belonged to a rare Y-DNA haplotype, but several alleged lines of descent belong instead to the *commonest* type of all. The first three generations (founder, son - he had only one - and grandsons) are all solidly documented, so the discontinuities occurred after that.
One documented line, and another that declined to publicize its documentation, matched the rare haplotype exactly - as did a third that can't show documentation that far back. So there *are* genuine male-line descendants.
One of the discontinuities probably happened in the fourth or fifth generation, because the fifth-generation descendant had two consecutive wives, and descendants of sons by each wife showed identical MISmatches. That is, they were clearly *his* descendants - and clearly NOT Thomas Plummer's. The Y-DNA evidence could not pinpoint it that precisely - only the paper trail could.
Thomas Woodson was the "only" person who matched the *specific* claim that the Jefferson-Hemings "affair" began *in France*. The general claim that there was such an affair has considerably more support than that.
Frankly, the most telling point is that Jefferson was on the scene nine months before each time Sally had another child - and she never conceived one when he wasn't there.
No one else, not even little brother Randolph (who is Suspect #2), has been placed in proximity so consistently. (And for that matter no one *ever* fingered Randolph as a suspect at all before the Y-DNA evidence ruled out the Carrs - who, as Jefferson's *sister's* sons, could not possibly have shared his Y-DNA, and didn't. And no, they don't match the Woodson line either.)
If *you* don't want to believe it, *you* don't have to - but disbelief is not the same thing as disproof.