"I believe it was a simultaneous transaction no matter when it was reported."
Simultaneous with what? Even though there are no footnotes on the Forms (Harness just filed one as well) I think it's generally understood that they are intended to cover the withholding taxes on the shares that vested on 9/1/18.
Even so the Forms themselves indicate: 3. Date of Earliest Transaction (Month/Day/Year) 10/12/2018