The wicker conch was there when I was a kid, 100%, but maybe it was regional?
Or maybe they realised getting rid of the conch would save them a million dollars in printing costs over five years (or whatever) and quietly removed it?
This one is the perfect example because I also remember it having the cornucopia despite it never being there in the official product. I would bet that the memory comes from the brain mashing together similar looking artwork from Thanksgiving.
Note: a memory is still a memory even if it isn't accurate, because memories aren't perfect.
Or it wasn't and you're just mistaken. You can find vintage underwear and t shirts on ebay from fotl back in the 70's and 80's right now. It isn't there. Also, snopes.com deemed it false.