I also owned a '70 LS5 Chevelle up until 2011 - during my attempt to sell it on eBay, some kind enthusiast let me know that Atlanta built Chevelles like mine had the broadcast copy glued to the back of the door panel (the only place I had not looked for it). To my very great relief, the copy was right there, absolutely perfect condition, glued very firmly to the door panel, with every last detail including the shipping info, dealer code, dealer and LS5 documentation that I needed to prove out the car: the dream of all of our collective Norwood production fellow Camaro owners. Although I have the dealer invoices on two of my Camaros (luckily the '68 Z is one of those two), I wish all of them had the BC's as well.
Keep on looking -
Steve