quote:
Your source says KP-271 is a good match for A.anamensis,yet they dont have a complete A.anamensis(correct me if im wrong)fossil to compare it to
You've not got it quite right. The site states that KP-271 is
attributable to A.anamesis.
The evidence is that the bone is probably from a robust australopithicine (as the analysis shows) and the A.anamesis name was coined to refer to the Australopithicine remains from that site and of the same age. There's no mention of any direct comparison between KP-271 and a humerus from A.anamesis.
Obviously it makes sense to conclude that KP-271 is of the same species as the other remains, rather than assume that it is from a different australopithecine.