I think Van that JW's claim that there religion is Bible Based is true.
Based only means that is the foundation you are working from, not something you are sticking rigidly to, as in Politics, a movement may be based upon the ideas of Karl Marx and therefore claim to be Marxist, but not stick to what were in fact his ideas close enough for Marxist Historians to agree with that Label.
That distinction is probably lost upon JW's and they probably think their weird and wonderful interpretations and twisting of Scripture is "the truth" ,which plainly is not so, but, regardless, those interpretations are "based" upon the Bible.
I have found it pointless and time wasting to actually try to debate Doctrine with JW's, but what I have done with some is reveal that I used to be a JW, and then say quickly, "There are several reasons why I am no longer a JW, a lot disturbed me deep down, surely there must be at least ONE thing that disturbs you about the JW Org ?"
Usually they come back with " No, I believe we have the Truth", then I say, (maybe) " Well one thing that disturbed and saddened me was the huge hidden Paedophile problem that is in the JW org". You are then away. But if something is more appropriate then do go for that, but rarely will arguing Doctrine work, their minds are shut fast against taking on board what is after all just another interpretation.