When something is "based" it only means that was the starting point; where it goes after that is up to the arranger. Sure JW's are "Bible based"; they started out using The Bible and ran with it. Where they are now is definitely not where they started, nor does it have to be, but they can still eithically make the claim. After all, they didn't begin with some other Holy Book then make a switch! They're "honest", they're just making more intelligent use of language than most of their critics and/or adherents.
Smiddy, my suggestion is that you work really hard to break the mental link between "Bible" and "scripture". Once that's accomplished there will be more work to do on "scripture", but it won't be truly productive until you really grasp that WT/JW's have (either artfully or ignorantly) combined two different constructs into one web of "Truth".
Sincere best wishes,
AB