No it is CASA's liability as they are the ones who approve the ops manual.
Talk to CASA. They DO NOT
approve flight manuals, they
accept them. For the very reason of avoiding responsibility.
Just like they used to tell us how much fuel to carry, not any more. That way when it goes pear shaped they can avoid responsibility.
Same goes for CAO48 and the standard exemption, they hate it and want to put the responsibility back on the AOC holder by way of FRMS.
With regard to pax weights. Our ops manual does provide for the PIC to require actual weights due to an obvious weight average problem. Don't we all round up on the RTOW and V speeds for this reason.