From a purely definitional standpoint, QA/QC is generally a post-manufacturing testing of product spec prior to distribution to catch out-of-tolerance product. What some here are referring to is a more holistic approach to quality generally called Total Quality Management. TQM integrates the design, planning, and production into the QA fold to ensure that mistakes are avoided as well as caught after they happen.
That said, both instances of the problem fermentations at DFH were, in fact, caught during routine testing during the production process. The 120 was closer to finished than the other beer, but both problems were identified relatively early, and efforts were made to bring the product back within tolerance.
I think the challenge here is that these guys are pushing the absolute limits of microbiology with some of these beers. If this were a manufacturing operations, you could merely engineer the product to spec with a margin of error. Because you cannot engineer the yeast to spec, there is no ability to build in a margin of error and thus, you can see that failure's are inherent in that kind of process.
It is kind of like Formula One racing vs. your local auto factory making cars. The F1 team has to push the limits of materials and engineering and often, they push too far and their efforts fail. The local auto factory builds to within engineering specs and hence, their products are generally reliable (think Budweiser).
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