Let's be clear that it was a success very much in spite of UB, not because of it. And there was still a cost--likely at least hundreds of person-hours spent fix

Let's be clear that it was a success very much in spite of UB, not because of it. And there was still a cost--likely at least hundreds of person-hours spent fixing other similar bugs due to UB (if not more). I worked in gamedev around the time this game was made and this would have been very much an ordinary, everyday kind of bug. The only really exceptional thing about it is that it was discovered after such a long time.