Does anyone know the truth about how far back they go?

80 hours is the anticipated window, but there are so many variables involved, that is merely guidance.
Of course the only surefire method of passing such a test would be to abstain while under the regime.

Don't drink like you were required to do... as well as avoid other forms of alcohol... then you don't have to worry about passing or failing.

As was mentioned...many people HAVE failed well beyond that 80 time. A few manage to cheat the system and get away with it for a few more times before they finally get caught.

The "how far back" can be determinant on past drinking habits, time from this last drinking to the time before. Your health.
And amount drank at the last time.

As noted 80 hours is an average, some pass at 70, some fail at 85. But a average used is 80. Thus why it is often called the 80 hour test