The easiest guy to hang is the one who signed the FSOs, courtesy of the all-encompassing how-long-is-a-piece-of-string "ensure that the contents of the flight library are correct" motherhood statement in the FAM, which if taken to the n'th degree would mean signing on 4 hours before departure and doing an effective page and amendment check of about 20 books. However ultimately they all screwed up pretty much equally IMHO. I mean, each one of them, including the front seaters, would've had an obvious opportunity to spot the error. Plus the previous sector's crew too.
Regardless of that fact though, nobody's perfect. Some of us are just lucky enough to get away with our screwups.
But it all comes down to the fact that there's a systemic problem with flight libraries in Qantas - one of numerous systemic problems the airline has had as a result of squeezing every dollar it can out of everything. There are any number of ways to make the system more robust and error-tolerant but they all involve spending money, and that's just not the modern Qantas way.