In QPMDISPXSec.cxx, the EM scaling variable (fEMScale) is applied both to EM and weak-NC events. And the weak-NC scaling variable (fNCScale) is not used. Presumably this is a bug.
The issue can be seen here: https://github.com/GENIE-MC/Generator/blob/master/src/Physics/DeepInelastic/XSection/QPMDISPXSec.cxx#L175C44-L175C52