How A Successful Response with Nothing Inside ?

Our New Zealand research job reports almost every request as successful, yet some saved files contain only a blank layout or a notice asking the browser to wait. The connection itself seems fine, so our current success figure is hiding a data problem. I do not want to buy more traffic while the output remains unreliable. What would you measure beyond the response code? We need a way to tell the difference between receiving a page and receiving the actual public information the report requires, preferably without building a separate rule for every minor design change.