I would concur with most of these comments -
The old timers may know the ins-and-outs of the doctrines and prophetic interpretations but newer JW's dont' have near as good of a grasp --
You can look at the progress of the home bible study books from the "Truth" book down the "Bible Teach" book. As you go down the line less doctrine is focused on. In the "Knowledge" book little time is spent on subjects like Hellfire and Trinity than in the "Paradise" book. In the "Bible Teach" book much of this further taken out of the main chapters and relegated to an appendix, topics like "Michael the Archangel" and "1914". The teacher is told that there is no need to go over the appendices unless the student has specific questions.
You can also look at the "depth" of internal JW books on prophecy too. The newer books on the minor prophets sheds a deep discussion of types and antitypes to merely focus on things such as Internet pornography and meeting attendence. Any book study conductor can attest to eyes glazing over during the study of the "Isaiah" book and to a lesser extent the "Daniel" book, as compared to some of the perceived "easier" study books.