My understanding is that the bolt is supposed to be movable by hand. As such, it might be a more appropriate location for a pin. I'm not sure threads are the ideal fastener at this point, especially if people lose track of them supposed to being loose and perhaps fall victim to a natural tendency to want to tighten everything up thirty years after the device first entered service.
Inscribing a torque setting and bolt specification next to the hole would have been a nice design touch back in the day, although it's not easy to specify a degree of looseness. Perhaps the manufacturer believed that only seasoned experts who knew everything backwards and in the dark would ever handle the bolts?
Trying to find out when the new threads were cut does seem to be a potential route to weeding out safety flaws that may crop up elsewhere. It's been asked before - it would be interesting to know (not necessarily on this forum) whether there were other seats in service with the same issue.
Hand skills are an issue, aren't they? In the days of additive manufacturing, you might be able to print a bolt on your desk, but do you know how to tighten it and whether to coat it with anything before you do?
Fortunately, there's not so may errors that focus on such a safety critical single-point failure of a part that's not tested, but still has to be right. But, it's still very sad, and it seems to be down to a loss of manual skill and craftsmanship in the pursuit of relatively modest savings.