As for the paper by Meave Leakey supposedly identifying the Kanapoi humerus as belonging to Australopithecus anamenis (Leakey et al 1995), the paper merely includes the Kanapoi humerus in a list of about 20 fossils from widely separated sites in Kenya (Allia Bay and Kanapoi), and with widely varying dates, that the authors chose to attribute to A. anamensis. The authors offer no justification for attributing the Kanapoi humerus to A. anamensis. Here is the only substantive mention of KNM KP 271 (the Kanapoi humerus) in the paper: "The distal humerus, KNM-KP 271, was originally seen to be humanlike, and it does show many derived hominoid features, including a marked median anterior capsular ligament tubercule." The authors make no attempt at all to show any nonhuman or particularly australopithecine features. They simply acknowledge the research showing it is humanlike, giving a citation to the relevant papers. It is clear that the authors included the Kanapoi humerus in the list of fossils attributed to A. anamenis simply because it was found in the same region and was about the same age as the other fossils--even though they acknowledged other authorities characterized its features as humanlike.
Leakey, Meave. G. Craig S. Felbel, Ian McDougall, and Alan Walker (1995) New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya, Nature 376: 565-571.