The WTS has discouraged "outside material" in its other study programs.
*** km 5/96 p. 7 Question Box ***
There is no need to supplement the information in the Knowledge book, bringing in outside material or additional arguments to support Bible teachings or to disprove false doctrines.
*** km 11/95 p. 1 par. 4 New Book Highlights the Knowledge of God ***
When you use this book to conduct studies, it is not wise to bring in outside material, which could becloud the main points; just concentrate on conveying what the book is proving in each chapter.
*** km 12/90 p. 7 par. 6 Being Taught by Jehovah ***
Care needs to be exercised when it comes to bringing in additional material. Some of the assigned material may involve only one or two paragraphs. But the material can still be effectively presented in the allotted time by reading and explaining the Scriptures, using illustrations, and so forth. Generally, we do not need to present material outside of what is assigned. The audience should be able to follow you in the publication the talk is based on.
*** km 9/77 p. 7 par. 4 Making Service Meetings Interesting ***
Where there is ample material in the article, make these points clear rather than bringing in much outside material.