don't think you missed anything bill!
Lots of engines run with dead sparks using double-ended HT coils. It's an easy way of running a twin with one contact breaker (or pick-up for that matter).
Does get folk into discussion about plug polarity and all that from time to time - ie which way is the spark jumping the gap on the plug. Some say, if they run opposite polarity, it's good to swap the leads round now and then and give them both a dose of 'wrong' way running, but I dunno. (In any case, unless there are any funny issues to do with inductance or something I don't understand, it should be possible to make a twin spark coil that delivers same polarity sparks each end, if the windings are correctly 'handed' inside. Not sure how the coil works on my one dead spark bike - it just does and long may it.)