Russia has the 9-13 instead of the 9-12 because that is the variant they widely used
The initial Mig29 models were not able to carry the 27er, the biggest reason why is that the mig-29 entered service before the 27er and that the 27er was primarily used on the Su27 instead, ontop of that they needed an avionics upgrade Iirc.
2- Also the windows for the TDD / proximity fuze seem to be long and longitudinal on the PL-12, while they are short and lateral on the North Korean missile.
So I think it’s likely that the external design was “inspired” by PL-12 (Like Fakour-90’s external design was by AIM-54).
Or perhaps the Chinese gave them some help with the design and some components; Though I find it unlikely as the Chinese don’t like the North Koreans very much …
My overall guess?
The external design was inspired by PL-12, but internally it probably / possibly uses some R-77 components …
It made no sense to equip the MiG-29 with a weapon that outranged the radar.
In retrospect, it may have been useful to have a weapon with better time to target, but that is something they probably hadn’t considered necessary.