Thanks for the update and for spotting the bug. Looking at the tables (without really knowing much about the finer workings) I suspected as much. I still believe that MOODLE is the way to go, though. The exam will be repeated if need be, and I'm bracing for impact
You might wonder why I didn't have a proper backup of the course. The problem seems to be that I imported the qs from 1.5+, but 1.6 refused to back up the quiz telling me "Cannot quickly initialize page: empty course id." (which doesn' make much sense) I know I should have done a database dump as the next best thing, but I didn't. That's my fault.