I believe the Auracana that are Rumpless (without tail feathers) actually don't have a tail for the feathers to grow from. I am sure that someone that knows for sure will chime in eventually.
You could check that out for sure. If that is the case, you have a rarer chick than you think as those are less common that the EE that many people seem to get when they order Auracana.
I have a Red that doesn't have tail feathers yet at 4 weeks..... But it is also slow to feather everywhere. The rest of my New Hampshires and RIR's and ???? Reds are almost fully feathered except under the wings and around the head. Mine came from Murray McMurray.