There's 2 possibilities with the PL-15 for the Block III.
1) The PL-15 was never going to be integrated despite assumptions of even the PAF's pilot community, due to whatever technical and/or budget reasons.
2) The PL-15 is being integrated, but this fact is not being publicized.
The question is, in scenario 2, what would be the incentive to hide this fact? Possibly because China does not want to pitch the Block III to other countries with the PL-15 package, because that may cannibalize possible sales of the J-10C. And if the PAF was getting it on the Block III, that would also make potential customers like Argentina complain about not being offered the PL-15 on the same Block. So it's possible the PL-15 on the Block III is an optics issue and it can't be advertised.
p.s. I also agree with
@siegecrossbow, the J-10C isn't a roadblock for integration itself, because the PAF actually wants both.