I don't even know where to start ! First would be that changing your drive belt has absolutely nothing to do with timing. Your husband was at the wrong end of the machine to not "reinstall something right", and have it go out of time! It's beliefs like this that get said and believed, and it's unfortunate because it doesn't help people that need help.
Second.."My machine requires an incident" to get out of time...I have no words !
I would consider hitting a pin, a set screw backing off or a huge thread wrap an "incident" ....didn't I say that???
I've been timing and repairing machines for over 40 years..I stand behind what I said. Done.