I have had this very discussion many times with my wife and mother in law since I have successfully faded and of course they always come back to me with the "company line" in Proverbs 4:8 which we all know is bs.
So this is how I have tried to reason with them:
I have no problem with the FACT that the wtbts (or any other organization) comes up with new understandings and/or teachings, especially when the shelf life of some of their 'old' understandings expire. The real problem is that the wtbts labels ALL of their teachings and doctrines "the truth" and since (by the very definition of truth) "the truth" cannot and does not ever change, labeling wtbts teachings "the truth" is a serious misnomer. So while it is not necessarily wrong to change a teaching or understanding when new information comes to light, it is very wrong for the wtbts to sanctimoniously and piously label their dogma "the truth" when in fact, it is only their best guess! Knowing the truth of this fact about "the truth" really does set one free!
just saying!