On the question of scriptural vs. unscriptural teachings, one way to approach it is from the standpoint of things the JW's themselves don't believe to be scriptural.
For example, unless I am very much mistaken, the JW's believe the "Book of Life" of Revelation 20 is not opened until the end of the millennium and this view follows directly from what they consider the "Resurrection of judgement" to be. (i.e. The vast majority of mankind are resurrected during the millennium and judged based on their conduct thereafter.)
However it is not at all uncommon for JW's to insinuate, imply, or even openly state both in speech and in print that having ones name in the "Book of Life" is about survival of Armageddon and that your name is put into this book via organizational affiliation with the JW's.
So an unscriptural teaching (By their own standards) is used for the sake of convenience as a sort of cattle prod vis-à-vis people they consider to be "inactive" or not otherwise doing enough.