Google up "rotor phasing." What happens is, that depending on "box" design and or wiring polarity of pickup coil, the trigger point can change. Remember, that with points, unless the dist was worn out or something wrong with advance plate, the points cam "the trigger point" was tied to the rotor. If it was in phase, it could not change
But with electronic trigger, if the wiring of the trigger is reversed, the trigger point moves because the magnetic trigger is a positive going spike and a negative spike. Only one of them fires the box. You reverse the wiring, the spikes reverse relatively, and change in time (rotation)
But the design of the box can ALSO affect this. We have no idea, over the year, who changed what in the box internal circuitry. If the "china" box triggers on positive spike, and the OEM triggers on neg spike, then you have changed timing and rotor phasing