Ed, it appears that the key difference is that the control is mounted in the exposed painted steel upper portion of the door inner panel, above the door trim panel in '67-'68, so it could be installed by Chevrolet without removing the Fisher-installed door trim panel. In '69, the door trim panel covered the entire door inner panel, all the way up to the glass opening, so the attachment of the control and bezel to the door trim panel had to be done before the door trim panel was final-installed in the Fisher Body Trim Shop.
The issue of "content" (who installed what) between Chevrolet and Fisher was a constant "war" between the accountants on both sides; Chevrolet HATED giving one of their parts to Fisher to install, as Fisher marked-up the cost of the part, added outrageous labor charges, and billed it back to Chevrolet as part of the "body cost".