Sadly, this is where modern technology hits the brickwall. The modern processes of printing means that printers don't need to employ proof readers, hence why errors show up.
Once a proof has been signed off by the customer (in this case WHFI) then the job goes straight to press. The difference being is when I worked in the trade (only few years ago) you would have a proof reader who would allot a certain amount of time before sending the final proof out to the client. The clients job wasn't to spot any error but to make sure they were happy with the pagination/layout.
How times have changed. :?