Just some numbers to think about. Years ago, old coils would do 20,000 to 24,000 volts. With higher compression and wider gaped plugs, more voltage was needed. HEI, maybe 28,000 to 32,000 volts. More voltage is harder to contain. HEI distributor caps are a larger diameter to help with this and better wires.
When Ford (bad word) first had electronic ignition the cap was smaller. With in a year or two Ford had larger distributor cap for their electronic ignition.
Back to your coil. Numbers exaggerated. Say you have 9-10 volts when cranking. The coil maybe designed for 7-9 volts gets a boost when cranking. Resister drops the voltage to 8.5 volts when running and the alternator is putting out 13.5 volts or higher.
So the coil designed for a 12 volt system and regular point ignition always has a resister.