I've heard doubters called nitpickers. Apparently as long as you call God by the name Jehovah, don't believe in hell, believe the number going to heaven is limited, believe in personally preaching in some form and the soul isn't separate and isn't eternal - nothing else matters.
If the GB touches any of those issues it would be a catastrophy for them. (with the exception of maybe the 144k being literal; I could see them saying it's a small number in comparison to the great crowd but probably not literal).