there's nothing in the Archives, unfortunately, to allow me to give you any definitive answer, but I'm guessing the first mention is in On Your Marks in '68 or '69. With full-blown detailing coming on line in '70 or '71.
i have this nagging feeling in the back of my mind (we are talking 40+ years here!) that those may have been the first that got splash, but that John had actually done a couple of earlier ones. Maybe we mentioned them retroactively?