I have unwound and rewound them, they are like thinner than a human hair. If the resistance changes like 1/100 ohm or wires short or you use the wrong CDI box it wouldn't take much for a little weak spot in the wire to burn up and open circuit. I think it's just a super marginal design.
I had one fry on the supplied master igniter box, one fried from a pietcard 2041, and one ran for a while on a jog then fried. Then I put the mbk pick up on there and it worked good until I forgot to torque it and fucked the keyway.
So then I had to go to the stock flywheel with the pietcard coil and jog box which ran great but was cutting out on the top end. I pulled it last minute before a rally and went points then I finally figured out my float was too low and bowl was running dry, fixed that and it ran great for one summer until the za ate itself trying to flat track race it.
TL:DR. I have no fuckin clue... Mopeds