You're kinda right, and kinda wrong.
If, at the start of the phase, a Location does not have any critical components in it that can take any damage, any critical damage done in that phase will transfer to the next location. To use your example, let's suppose that both the Shoulder and Upper Arm actuator took critical damage in prior turns, and there's nothing else in there save Endo Steel. You would roll Determine Critical Hits, and if you get anything, those Criticals would get resolved in the Left Torso.
However, the "12" result for the arm does *not* transfer: you're not rolling Determine Criticals in the Left Torso, you're rolling it in the Left Arm, so you resolve the 12 result, which is limb blown off. A limb with 0 internals left, so it can't be used as a club, but the Left Torso at least does not suffer Critical damage.
I don't think I've ever seen that happen.