I have the double 60" Fairmont Windwood vanity with two Kohler Archer sinks. I just checked and front to back the vanity is 21" (plus 3/4" for the drawer front). The countertops were just put on yesterday - here's a picture of the one in the other bathroom, which is a 48" single, but it's otherwise the same (all Fairmont Windwood, all Kohler Archer sinks).

I just looked at the dimensions of the Archer - the 19-7/8" is the side-to-side length, not the front-to-back width, which is only 15-5/16".