The question. Is all Watchtower articles, books, etc. inspired by God as the Bible was? The answer is no. Think of how many articles have been published in the Watchtower and Awake. I don't have the total count, but I guess thousands. Many articles in these publications deal with daily news, and other needs that people encounter. But what about the articles with Bible topics?
Witnesses use the Bible to decipher the Bible. A good example is the understanding of the book of Revelation. Many facets of this book can be understood by comparing with scriptures in Daniel and Ezequiel.
If the Watchtower articles were inspired, then that means we would have an extension to the Bible and this is not possible. Jehovah made sure that we had the Bible as our guidance.
Why do Witnesses then claim that the articles come from Jehovah?
Well I will illustrate: What does the White House spokeperson do? Well he addresses the media on many issues concerning the President. He represents, at that point, President Bush. So what he says, is as the President were saying it. Can the spokeperson make a mistake and say something he shouldn't? Of course, then the President would ask "what did you say that for?, you should stick to what we've told you". Then the spokeperson would go in front of the media and make the correction of his statement.
Similarily, the Faithful and Discreet Slave represents Jehovah here on earth. Their publications are based on the Bible, so it's as if Jehovah were saying it. Can that slave class make mistakes? Yes, and Jehovah is probably thinking to himself "Where did they get that from? Who told them to say that?", then he guides them back to the scriptures so that they can make the proper correction.
In that sense, the Witnesses have the guidance of Jehovah by means of his holy spirit.