before they will know

[sitifan]

Then, even when 2000 passes, we'll still have people upset for three-and-a-half years more before they will know you were wrong -- like all those who have come before you purporting to prove Christ's coming was at hand. (my bold, quoted from 1999: A Novel, by Stanley C. Baldwin)
https://www.amazon.com/1999-Novel-Stanley-C-Baldwin/dp/0830813632
Is the modal verb "will" obligatory, optional, or redundant in the before-clause?

 

[emsr2d2]

In this sentence, it's optional. I wouldn't use it. Mind you, whilst it's not for me to argue with a published author but I wouldn't have used "more" either.

... even when 2000 passes, we'll still have people upset for another three-and-a-half years before they realise you were wrong.

 

[sitifan]

In this sentence, it's optional. I wouldn't use it.

It's crystal clear that, when we're talking about sequential actions, we do not use the future with temporal conjunctions: He'll get here before she comes, not he'll get here before she will come.
How come "will" is optional in the before-clause of post #1?

 

[jutfrank]

The auxiliary will adds to the predictive nature of the utterance.