There's no problem with newspapers writing a stock pieces for either eventuality, and yes, sometimes someone will accidentally press the wrong button, and the wrong version might go up for a bit.

But the wrong story they put up wasn't a generic piece. It has specific claims about specific actions, which obviously didn't happen. They made claims about how the defendent acted upon hearing the judgement (Knox "sank into her chair sobbing uncontrollably while her family and friends hugged each other in tears"), it had quotes from Italian prison officers, etc. It was clearly an outright fabrication. They wrote, in detail, about Knox' reaction to the verdict, before the vedict was handed down. And we only know they made it up because they cocked up.