Mistakes happen on any line. It's inevitable. That's why there's an inspection stage at the end of an item's production. If the product is inspected and found to be defective in some way, the quality control process should reject that item and feed back the information to hopefully ensure it doesn't happen again. Quality control feeds back to quality assurance.
When quality control fails to catch problems, a product is shipped that is not up to scratch and which may impact the user's ability to use it as intended. There's a very good argument that quality control is the most important function in any production line—it doesn't matter what mistakes are made as long as they don't leave the factory.
On a completely unrelated topic, the fret-ends of this guitar have been bevelled at too shallow an angle. The end of the bevel is actually past the first string. Playing pretty much anything on this guitar's top E-string causes it to slip off the side of the neck. It's impossible to play well.
I've seen this particular mistake on more than one occasion over the last year or so, though. All new instruments. One repair guy's evidence does not a conclusion make but I suspect a process failure somewhere.
As a bit of good news, I'm informed that the manufacturer of these guitars has taken feedback on board and is concerned about any lapses in quality. Fingers crossed that this will translate to improved axes.