You guys are WAY overthinking this with all the talk of formulas and flux. The ignition coil is an inductor which is the electrical equivalent of a flywheel. When current is low and you try to increase it, an inductor will increase resistance to the circuit to try and keep current low. When current is high and you try to lower it, an inductor will increase voltage to the circuit to try and keep current high. When you open the points on a breaker point ignition it's equivalent to shoving a broom stick in the spokes of a spinning wheel to stop it. It's the same analogy with [non-CDI] electronic ignitions only you are using a steel pipe instead of a broomstick.
When you break the primary current, the voltage of the ignition coil will rapidly rise until it can get current flowing again. The coil does not care where the current flows. Electricity will always take the path of least resistance so EVERY component of the ignition must have adequate insulation to contain higher voltage that what is required to fire the spark plug. If the spark gap is not the weakest insulator in the chain then the current will flow elsewhere and the engine will not fire.
That brings us to the real trouble with refurbishing old ignition coils. A common failure of old ignition coils is a breakdown of the secondary insulation. You won't see this with a low voltage ohm check. Even a megger can miss it. When you see a coil advertised as a 50,000 volt coil, all that means is that the secondary insulation can handle 50,000 volts without shorting out, not that it will put out 50,000 volts. If the spark plug only needs 2,000 volts to fire then the voltage in the coil will rise to 2,000 volts at which point current starts flowing again so the voltage stops rising (it actually drops significantly since it takes less voltage to maintain the spark than it did to initiate it).
The voltage rating of the coil (secondary insulation) degrades with age. A 10,000 volt coil is more than adequate when it is new but now it's 40 years old and can only handle 5,000 volts. The engine will still fire up, idle well, and go down the road without a hint of trouble because the spark plugs need less than 5,000 volts to fire. However, when you crack the throttle you are allowing more air into the engine which means that the dynamic compression is higher and the spark plugs require more voltage to jump the gap. Now you have a funky hesitation that you will likely blame on the carburetors because, "it had a nice blue spark when i pulled the plug." I've fallen for this more times than I care to admit.
Do yourself a favor; just buy a new ignition coil from the start.