Earlier designs often relied on punch proof dial spindles. In this case, the door cover and lock back cover give some resistance to a punch attack, not to mention the required force to separate the wheel post from the case. The fence lever would twist and bend as the wheel pack is forced out of the lock. Or the lever screw might shear. In the first case, accessing the lever to retract the bolt is possible, although difficult. Second case accessing the bolt directly to retract is also possible, although even more difficult. So adding the blocking plate pretty much foiled this type of attack.