There's a scandal going on in my state right now. St. Paul crime lab, which serves a good chunk of the 16th largest metropolitan area in the US, was not accredited and was reportedly so sloppy that they are having to retry and retest a tremendous number of samples. The local media coverage has shined a spotlight on the fact that a lot of labs aren't accredited and there's no law requiring them to be.
DNA is the tip of the iceberg for labs. The majority of the work is drugs, guns and fingerprints.
The most glaring example I can think of is a 60 minutes story from a numbers years ago. Crime lab testified a DNA match, but upon further review post conviction the lab tests showed that the blood type didn't match between samples. So why wasn't that a red flag for the lab? Well they interviewed the former head of the lab and his position was that it was the responsibility of the defense to deal with. The lab is simply stating an opinion on the tests.
The AC sounds like they run a tight ship. But I contend that's the exception, not the rule. In particular with City and County run/contracted labs.