I think that the schematic is simply drawn like that for simplicity. The slave coils can be separate coils or they can be multiple windings on one coil. By the look of JB's pics he has 4 transistors in a row per board, so he probably has 4 filar coils, meaning each coil has 4 lengths of wire. However one of them (the master) would be 5 filar to accomodate the trigger winding.