I think it's yet another of the myriad failures of conventional assessment approaches--content review doesn't fit anywhere in there, and of course, when it's done in a highly regulated and institutionalized way, it's worse than not doing it. So we just cross our fingers and hope. Mostly I think our hopes are well-realized--this is a problem that comes from a very small proportion of teaching faculty. But given that we know that teaching well across the range of a discipline (and beyond) takes active exploration of areas of knowledge outside of a specialization, we do very little to ask that of faculty or reward them when they do it.