Auracanas are rumpless birds and are small. I think the hatcheries sell mixed breed birds that may have some auracana in them, but the Ameraucanas from hatcheries I've been told are really just a mixed breed(easter eggers).
I have to tell you that I have seen Ameraucana pics and my "ameraucana" chicks I picked look the same. They have ear tufts and beards. I really think that I'm just as confused as you are. I posted pics and I was told that they are easter eggers. I don't know but I have one that is smart, she's a few days old and she tries to escape whenever she can. All three look like chipmunks.
Araucana - standard of perfection calls for tufted and rumpless birds (no beards or tails). Altho some breeders use tails in the breeding to keep the backs longer. There are also clean faced araucana used in breeding, because the tuft gene is lethal and folks end up with high death rates at hatch because of this gene. Eggs s/b blue, but blue/green eggs are often seen due to working to development the physical features of the breed instead of improving egg color. There are standard colors for this breed.
Easter eggers are what most hatcheries are selling folks. These are ameraucana and/or araucana crossed to completely other breeds of chicken to create a chicken that can have any color plumage and lay any color egg. Egg colors are typically blue, green and brown (pink), but can be any shade of them as well. Plumage color has no regular pattern and even if bred back together will never produce the same colored offspring.
A true breed always produces offspring of the same color and characteristics. Even if chicks looks oddly similar, there is no guarantee from a hatchery that the chick will meet the standard when fully mature, nor that it will breed true.
You can go to my website to see the differences in all three breeds as well with pics. I raise bantam buff ameraucana, EEs and various colors of Araucana (including non-standard colors).