Tom, I think SP means spark plug, but it’s the same thing in either case. I believe you are correct in the way these coils are constructed.

Huntleybill, the brittle soldered connection means you were not quite up to temperature to make the solder stick. You are right to be concerned about overheating. I used my iron on the 250W setting and removed it as soon as I had good contact. A hot iron can direct more heat quickly to a single spot. You do have to be careful. This is why I measure continuity before and after. Melting plastic is bad, but a little is probably fine considering that the plastic surrounds the nubs. It would be worth wiring them up and trying it again.