2OP:
I guess the full story is that for different reasons aeronautical charts get reprinted somewhat frequently so the magnetic variation and it's depiction is being continiously updated with sufficient accuracy.
Using an oldish (2 years) chart and not applying the "annual rate of change" for MV is in practical terms acceptable, as in short distance (<30 NM ?) from the Navaid the angular error represent only a small physical displacement. On a written test, different story.
cheers, FD. (crossed post with BEagle)