You raise an interesting point, I guess I always thought they would be pretty good at what they did. I do remember a book study and some subtle changes were pointed out by some who had earlier books (dont remember the publication now) I was surprised at the time being a child, thinking they cant make mistakes - now i realise it was an unanounced update. Someone here pointed out recently that they still have information refering to the generation teaching - and how long has that been changed! Your right they are sloppy.
CS 101