Seems to me that we have a series circuit here. Battery terminal, switch, coil of wire, resistive element to limit dc current flow during coil initialization to protect the points from excessive pitting, points with condenser across them for the same reason and noise reduction, and a battery terminal.
Since current movement is the name of the game, the current is common throughout the circuit because there is one common wire which carries all of it.....except for the point-condenser interaction.
Seems to me it is more of a convenience in the design as to what is located where, and in the case of a 12v coil whether or not an external resistor is required. If my memory serves me correctly the 12v coil is just a 6v with an internal resistor; whatever it takes to limit the current to 2-4 amperes or whatever is the magic number to get the right energy in the circuit and not burn up the points.
The purpose of the whole circuit is to fill up the coil with the correct amount of energy required to fire a dirty, worn gapped, plug. As I recall it takes about 0.15 joules (watt-seconds). That energy is derived from energy stored in the coil during the charge cycle (points closed) through the relationship w =1/2 L(i squared). L being the inductance of the primary coil winding and "i" the value of the current through it at the second the points open. Then it's just a matter of setting the desired turns ratio for the secondary voltage desired at the plug.
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