[crusty]

It's not proof of anything, including not proof that it works. The catalytic converter was stolen off of my father's car, was replaced, and then was stolen again. When it was replaced the second time, he very seriously considered paying for anti-theft devices to accompany its replacement. In the end, he chose not to purchase or install any anti-theft devices. His catalytic converter hasn't been stolen since. Just as this is not proof that choosing to do nothing has prevented subsequent theft, if he had purchased a device, the absence of a subsequent theft would not be proof of its effectiveness.