I think I may be able to shed some light on some of the variances.
I grew up about 15 miles away from the Norwood Assembly plant. From
time to time various aspects of the plant would make the local news.
It was a large enough employer that the chances of knowing a family
member of one of the workers was good. In addition to the factory
workers, other locals were indirectly contracted by the plant for
various things. So, talk of the plant and it's problems would be
heard from time to time.
In high school, I also worked as a line boy at a local airport and
fueled small and medium sized cargo planes.
What was very apparent was GM's desire to maintain the production
line at nearly all costs. It was common for those cargo planes
to be moving parts for the plant, and from many locations and suppliers.
So, it's my theory that GM would have used an alternative supplier
as needed in order to maintain the production line.
Joe