You'd think there'd be some plausibility checks in bills like this based on history. This sort of thing makes it into the news several times a year, and I'm sure they are very expensive to resolve after the bill is sent. If it gets trapped first, and reviewed, it can be corrected and then sent at relatively little expense. Automated systems have all kinds of exception reporting, and it makes sense that this would be one of those checks.
Even a basic check, like a residential customer with a multi-thousand dollar bill should trigger something, even without looking at history.
