I hadn't considered a running change on the decal (and should have)--that's entirely possible. The flap air cleaner was also used through 1973 on 340s (and throughout '73 on 440s) so it is possible that's a '73 air cleaner. Crap got swapped around a lot on these cars. I tossed my '73 (non-flap) in 1988 in favor of a hot-rod chrome unit, then got a junkyard '73 340 air cleaner so I could keep my fancy POS when I sold the car (I was 18--cut me some slack :p).
The big problem is that so many of the reproductions are just plain wrong. Decades ago, close enough was exactly that, and now some of those 35-year-old decals are taken as gospel. And as I mentioned, the parts-counter decal was slightly different than the one used on the assembly line.
Hoping against hope, I just went and checked a '74 dual-snorkel--which I'm sure had the decal you seek--but whatever hack chopped off the snorkels and painted it red (it wasn't me this time!) also scratched away the decal.
I have a friend with an unrestored '72 340 Charger. I'll see if he can get me a picture of his air cleaner and tell me his SPD/sequence number. It may well be a midyear thing.