I apply a mixed approach. Unless the Tables specify "Superficial" I treat it as "No Effect" per the Peckham Points Tables unless they have a separate entry such as "Each Additional Engine Hit." With Wounds, I record them as the Wound Typ assuming it still does the same amount of damage to the Aircraft. So, for a LW on an already KIA crewman I still record the Peckham Points for the LW.
I play it same way.
Do not confound damage to the aircraft and effect on the crewman. A LW still does 2 Peckham points whatever the current status of the crewman.