The mistake was an incorrect specification. A programming tool can't identify that you've made the wrong thing, which is why we need "rigamarole" to validate the spec. That's what the systems engineers are for.
Had they validated more, they would have realized they made the wrong thing.
> the main computer interprets the data as real navigation data and considers it as an indication that the rocket is wildly off-course
Not clear what sort of magnitudes we are talking about but saturation could have worked here and avoided the problem.
But an exception handler could've helped too.
> The code wasn’t necessary after takeoff, it was only part of the launch pad alignment process.
A supervisor for this task could have decided to ignore an overflow fault after launch.