I think it starts from a bit of lack of communication on both sides, for example the basic weight of the plane is almost always wrong. That can really only come from our company, to be passed on to the handling company that subsequently works out the load sheet. But really, there's not a lot of difference at the end of the day between 11 flight attendants and 13.
We also operate about three or four different variants of the 747-100/200, so there's the inevitable differences there, too.
FWIW, 'our airline' does not ever provide computer load sheets, they're always done manually by the F/O and checked by the Captain. That's almost invariably the case, even when given computer load sheets given to us by just about anyone.
They are also not used to handling a 747, but since it's computer generated I guess it shouldn't really make a difference as such.
An example there is we typically load the freight about 40/60% front to rear. Got the load distribution last week and it was 60/40! I did a manual check (of course) and it was well within limits, but if they'd put the freight where it was supposed to be then the CG would be well more towards the middle of the limits. If it was even close to have being a problem we would have told them without hesitation to take it out and start again.
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Motion coming on!