Trust me, that chick is not rumpless.
Rumplessness is rarely to never found in hatchery EE's, and is indeed an Araucana thing, while beard/muffs are indeed an Ameraucana thing. The EE's from hatcheries were from the same stock today's Ameraucanas root from though, however one was bred for specific traits, the other just as is, a mixed lot.
Anyway - A rumpless chick by now would have an obvious nice curving slope of a rear; I've had an EE who was just like yours though, it was a boy, and for the longest time I thought it was rumpless, then one day developed a small tail that pointed straight down, and as he grew older, it got more erect and upright, and, once mature, he had a normal tail like any common EE. That chick of yours though, wow, BIG beard/muffs!
As for muffs/beard, no such thing as triple genes. All traits are carried with two alleles, two copies, really. Muffs/beard are a dominant trait, so, even if a bird has only one copy you'll still see them. If he has both copies the beard/muffs will indeed be more full in shape, but, not that much more different, the main difference is that both copies will allow it to breed true, in other words, you won't get unwanted random clean faced or small bearded chicks down the road. Only one copy and that can happen though.
Tufts are different in that even though they too are dominant, you can only have one copy. Two copies, and you've got a dead bird before birth. And like with muffs/beard though - No copies, and you've got a clean-faced bird.
I think your chick has a really big beard/muffs for a separate reason than having one or two copies of beard/muffs genes, although I gotta say it is very likely he has both copies. (aka Homozygous)
