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I don't know about Ford, but the Dodge 5.7 Hemi used 1/2 as many coils as plugs and the extra spark is just a waste spark to allow that little trick of using 1/2 as many coils on a crank triggered ignition. The coil doesn't know if it's firing for combustion or waste, it's just firing, because the single shock is just split into 2 plug wires. I would expect it to show as a misfire on both cylinders it services if it fails, but also that random misfire code usually shows up if there are any signs of rough running even if it has nothing to do with a misfire.
On that 5.7 Dodge they use 2 plugs per cylinder and then cross them over to separate coil packs. You basically never will notice the loss of just one pack as you only lose 1 of the 2 plugs on 2 of the 8 cylinders. Heck you could lose 4 of the 8 packs theoretically have a good spark in every cylinder still. Then they changed that at some point I think to eliminate the plug wires, some of the early generation guys use "shorty" wires to also not have a mess of crossover wires on their Hemis.
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