> Evidently not though

Bolts can be loosened by the physical and thermal stresses of use if there is a design flaw. So it’s not evidently an assembly QA problem.

The plane that lost a plug mid-flight was only two months old though. A design problem probably would have shown up in an older one.

> A design problem probably would have shown up in an older one.

Maybe, unless it required really specific conditions that have only occurred for this one or also required some maintenance snafu that also had nothing to do with Boeing assembly QA. We don’t have enough data to establish anything as the most probable explanation yet.

According to the linked article: at least five aircraft. So, not unique to this one. Or the one that blew the door out.

Surely you've heard of reliability bath-tub curve.

Uh, first part of the bath tub curve is driven by manufacturing defects... That's not a counter point at all.

That curve applies to design issues as well, they are more likely to be found in the very beginning (teething problems) as well.