Do you have just the one male? That's crazy odd on the rumpless issue. Of the myriad of issues that the SPR in general are plagued with, this is a new one to me! Don't count those pullets out just yet; though they lack that nice, flat back we like to see in the older juveniles and adults, they are clearly "on alert" in the pic. That nice tail life may come later. I know with my line, it's a full 20 weeks before I even begin to see that females' tails really start to show me where they are headed, and that is quite early.
I find my 16 week old SPPR are slow in the tail department as well. Actually I think this picture is 2 weeks old, so he'd be 15 weeks.. but still the girls are quite developed where the boys are just, not.