sorry - been travelling for a few days.
to answer the question "Can / Should EXO be placed over a coating like OC, CQ, C1? "
yes it can - it will bond to all of this class of coating ie covalently bonding silicon dioxide/carbide coatings.
and of course it should :lol: seriously. not absolutely necessary but the layer of exo will give you all the nice things you can get from this tech such as slick finish, wet look, superb hydrophobic function and treated right (use pure shampoo not caustic cleaners such as snow foam) this will continue functioning this way for as much as 2 years on an every day car.