Probably not, it would come down to the manufacturing process and equipment available. There was already a black gun in the blackout booth used for the firewall on all cars (suppossed to anyway), Why would they have a second black gun on hand that they would need to use on the rockers of all style trim cars (probably 30% of production) and on Big blocks (probably 15% of production. Whatever they used on the firewall (gloss, semigloss, satin) is more than likely what they used on the rockers and on the tail panel. More colors mean they need more piping installed to carry the paint, or local tanks in the booth to hold the paint, all for almost zero gain from a styling point of view. did it really matter to GM or the customer if the paint was semi gloss, or gloss? No, thats just the way it came.