At the most, the Society could Biblically claim that people in the last days will get 120 years of warning like they did in Noah's day
I've been out for a while now and I'm getting a bit rusty on my JW doctrine, but didn't the WT say that Noah preached for 40 years?
Edit: I found an old thread I started on this topic years ago and there's a refefence in there to a WT where they say Noah preached for 40 years.