Well anything done directly to influence bugs/kloc is bound to throw the whole thing off. I think the parent here was mostly interested in discovery rate, which

Well anything done directly to influence bugs/kloc is bound to throw the whole thing off. I think the parent here was mostly interested in discovery rate, which also can be influenced by hiring/firing test and QA, or for that matter gaining/losing customers that use the product. And everything being mostly equal, it could be a reflection of code maturity more than anything. The more mature product may have a higher bug/loc ratio only because more of the bugs have been found. Which is why I mention there are metrics, but they all seem to have major problems.