A more convincing argument would exclude other possible causes. For example, were the inspections run badly? Were people inadequately trained? Were inspections introduced when people were too busy to learn how to do inspections?
The Post Hoc fallacy is a special case of a more general type of fallacy — the fallacy of the false cause. In Post Hoc, the apparent causal connection relates to the timing of the two events. But connections can also be unrelated to timing:
All of the projects Gerhard has managed in the past few years have been late and over budget. Since people now believe that Gerhard was the cause of the overruns, he can no longer get assignments as a project lead. Nobody seems to remember that each of Gerhard's project sponsors had either reduced his budget or expanded requirements so many times that no project manager would have had much of a chance to perform well.