" Bible based does not mean biblical." That is the point ! Not that I see it as vital that Theology or Christology should not have evolved since the bible was written. Those two things evolved over the time the N.T was written !
But, the "Bible based" thing is typical j.w Org. double speak, to the public and the average J.W, those words mean the beliefs can be shown unequivocally to be in Scripture, and as Van-the-man has shown , they re NOT !
The Quran and Book of Mormon are just as "Bible based" as the J.W's beliefs are, which means they are not Biblical !