My point is simple....you do your job properly....and carry out the preflight planning and related procedures and you cannot be found at fault.
The Pilot has to rely upon the data he is provided being accurate re Weight and Balance and Engineering actions that lead to the Aircraft being presented as "Serviceable" and safe for flight.
Absolutely the Pilot's actions will be examined but it would be an absolute defense against civil, criminal, or administrative action if he can demonstrate he took the proper actions.
Likewise....as in this case.....it is the Engineers who signed on the dotted line that would wind up carrying the bucket (or should).
As part of the Certificate of Airworthiness....the aircraft should have been inventoried, weighed, and a CG calculated per the Authority's Regulations.
Once that is done....that data is entered into the Aircraft Documentation.
The Pilot's calculation should have confirmed the Mission Equipment and other items were accounted for when he did his own W and B calculations prior to flight.
I cannot remember ANY time a Line Pilot has queried the basic weight and balance data for the RFM/Aircraft Records as part of his daily preflight preparation.
I have as you have said....challenged a weight and balance report AFTER discovering unlisted items on the Inventory (four sets of Speakers in the cabin overhead behind the sound proofing and some other items)....and was very dismayed by the Company's reaction.
But then.....knowing the Company in question that really did not surprise me.
When one finds a tail rotor pitch change link dangling loose after a Tail Rotor change....and the Logbook signed off as Test Flown and Released for Service.....and neither the Engineer or Pilot involved got reprimanded....what's a bit of extra kit on the aircraft and not on the W and B Documents.