I thought the torque thats retaining the nut is acting on the threaded portion of the bolt in the nut. The bit sticking out is irrelevant. The reason for 1 1/2 or 3 threads is to ensure that there is some reasonable standard for providing an adequate torque surface. As for nailing you for your signature in the event of accident/incident; if the work was accomplished per a manual, and you can show that manual reference then you did as instructed by the OEM or your Engineering department. If the fastening is significant enough that they dont want the nut falling off, they'll use one of Coriolis' split pins.