I do not know what particular treatments the cars that you are describing received for the 1964 World's Fair, and you may know more than anyone else since you were the author of that article in the most recent Mustang Times magazine.
However, I do have it on very good authority that back then, a car would be designated to be a special finish car that would be used in special presentations like a tour by the factory, or a special car for show room presentations, and I am told that the fit and finish on those cars did not even resemble that car of the very same make, model and color sitting out on the sales lot. These vehicles were painted with a finer, more meticulous eye, and the employees were instructed to be sure that all the lines were straighter than normal, no flaws or imperfections were tolerated, and basically , they received the "microscope treatment". I know that this is not much, but maybe it helps a little.
Hhhmmmmmmmm.....wonder if this is where the MCA came up with "councous" standards ???
PS..I just got off the phone with my "authority" who was in charge of the paint department at the Atlanta assembly plant for 32 years, and he also informs me that when a car was pulled for "special" treatment, they (he) personally pulled the interior appointments, the fit and finish for the chrome parts, anything and everything that the customer or the VIP the car was being built for. No scratches, no nicks, no chips, no oversprays, nothing was overlooked on these vehicles. Anything visible to the eye was given preferential treatment on these cars. A higher degree of quality was the standard for these "special" cars.