While idling thru a used bookstore in Salem this week, I stumbled across an older copy of Hubbard's Dianetics: The Modern Science of Mental Health. (copyright, 1950; 21st printing dated November, 1971). Since it was less than a dollar, I decided to pick it up, & satisfy my curiousity about what changes he made to this work in the 1970's.
I have to admit right off the bat that I have done little more than skimmed the book, so I cannot offer a decisive answer to this question, but even a cursory comparison shows that Hubbard made one consistent & important change to his work: every place where another author's name appears in this work has been omitted. Reading the later version of Dianetics, I was led to assume that Hubbard invented the entire opus himself, whereas the earlier version is full of acknowledgements to other Dianeticists & co-authors!
The first & most obvious place this occurs is in the dedication. This version is dedicated to "the famous Magician, George Wichelow, England's First Dianeticist". The later version that I have (copyright 1993) is dedicated instead to Will Durant.
A glance at the Table of Contents shows that several appendices written by various authors, as well as the well-known introduction by J. A. Winter, MD, are excised from the later edition. While it is possible that this excision was done out of concern for copyright, two more prefatory essays were removed: a "Note to the Reader" signed by the "Board of Directors, Church of Scientology", & a Synopsis of the book signed by "The Editors".
The subject of these appendices are worth describing briefly, for the many in ARS who have never had access to earlier versions of this work. The first appendix is a extended quotation from Will Durant's book, The Story of Philosophy entitled "The Philosophic Method." Durant's point in this passage is summarized by the concluding sentence: "Science gives us knowledge but only philosophy can give us wisdom." The purpose of this quotation is unclear, since Hubbard early on in this book derides philosophers for their theorizing, & praises engineers for their practical knowledge.
The next one "The Scientific Method" is by John W. Campbell Jr., the famous science fiction editor who mentored Hubbard over the previous 15 years. It is an intelligent essay, making the point that scientific knowledge comes from questioning assumptions & studying the evidence & NOT the interpretation of observed phenomena. The relevance of this essay in a book where the author draws sweeping conclusions from little or no evidence is likewise puzzling.
The final pair of appendices are by D.H. Rogers, each an essay accompanied by a flow diagram, explaining the Dianetic model of the mind. The two diagrams have dates on them for the months of January & February of 1950. Although short, they are ladened with jargon, & do not make sense after a quick reading.
If these deletions did not suggest to the objective reader that this work has received the attention of more pens than only L. Ron Hubbard's, there is one footnote that vanishes from my later edition that is clear evidence for this theory: In the first chapter to book two of this version, "The Analytical Mind and the Standard memory Banks", there is a footnote with the initials JWC that explains the thesis "how the analytical mind can compute perfectly." Locating all of the footnotes in this work & comparing them with the later version of Dianetics that I have, this is the only footnote with someone else's initials on it, & also one of the few not reproduced in the later version. Most of the other deleted footnotes are notes alerting the reader to the fact that a given topic is dealt with more fully in another one of Hubbard's books (all of which were written after Dianetics), although one -- a gloss on the word iatrogenic -- was removed, & a second footnote defining the word "auditor" is silently moved into the glosses that decorate the later version of Dianetics.
This unique footnote suggests that John W. Campbell rewrote at least part of this chapter, & it was removed to obscure Campbell's part in this book -- making it appear as if Hubbard had written it all by himself!
Other than this consistent erasure of other hands from this book, I have not been able to identify any other significant changes to the text between the two versions. Comparing the two versions, I found it a simple matter to co-ordinate the location of passages between the two: paragraphs, for the most part, have not been reordered, & the beginning words were kept unaltered. However, the addition of the footnotes I described above, alerting the reader to later works by Hubbard, suggest that it is possible earlier revision were made to this book.