So yours is a 72 340 Demon? A little context would be nice. I have helped restore a few and had a few survivor 72 340 Demons and they all had Dart on the deck lid...
So I asked Rick Ehrenberg, and he said that all of the factory literature showed both Dodge and Dart badges are supposed to be included, so my apologies to you, you were correct that all '72's are supposed to!
That said, mine did not have holes in the decklid for the emblem(s), and I've seen many that don't. So that makes me think maybe there was a badge shortage or something. I can't remember where mine was made, that could be a factor too. Rick also said that there was a revision to the paperwork so it's possible they revised it midyear or something.