Not so long back I was tasked with checking the details of a used helicopter for a potential buyer. When it came to checking the empty weight of the aircraft I studied the factory weight and balance schedule (in the individual RFM) to calculate a few typical mission profiles. Whatever calculation I did, the C of G was well outside the envelope. Even the zero fuel figure, with one pilot up front, was 4" outside the fore/aft limit. I asked for the aircraft to be re-weighed and this showed that the original factory figures were nonsensical and were nowhere near reality. I used the new W & B schedule for my original calculations and found the aircraft fore/aft C of G to be as close to neutral as any could be.
Two worrying things:
1) The factory figures should have been absolutely correct in the first place and whoever did the weighing should have noticed what must have been large discrepancies from normal figures on that type of aircraft.
2) I was probably the first person to ever carry out a mission W & B calculation on that aircraft. If the original figures had been correct, it had been inadvertently operated for almost four years with a C of G approximately four inches outside limits!