yr right, you appear to be labouring under yet another misconception. You appear to believe that the spark occurs at exactly the same instant as the points open when the engine is running. It doesn't.
It takes time for the collapsing primary current to cause the voltage in the secondary to build sufficiently to arc across the plug gap. During that time the crank is rotating. It's not long, but it's long enough for the crank to rotate half a dozen to a dozen degrees (depending on RPM).
The mathematics is quite simple and the reality in operation is measurable (and has been measured).
Leave operation to the experts.
PS: You are correct on one suggestion - the manufactures do take this into account in determining the static timing spec.
Last edited by Creampuff; 13th Apr 2014 at 10:33.
Reason: Added PS