OODAD:
All paper and pencil self-report tests are quite inaccurate because people are very poor judges of their own personalities.
But the Myers-Briggs is extremely flawed in its construction.
If you want to know the specific ways MBTI fails read this http://www.indiana.edu/~jobtalk/Articles/develop/mbti.pdf
You said "Nevertheless, the fact that cult members remember themselves as being different prior to their cult indoctrination does prove the effects of the cult involvement on their personality even if it does not accurately reflect what those actual changes are."
That statment doesn't prove anything "if it does not accurately reflect what those actual changes are."
One reason people join cults, go into therapy, read Self-Help books and change religions is because they are not happy with themselves and they want to change in some way. Alcoholics Annonymous also comes to mind as an example.
People tend to introject the leaders (exemplars) in their organizations. Some people are more vulnerable to this process than others. These individuals sometimes need quite a bit of therapy just to gain an identity separate from a parent they feared or respected.
Hassan is correct in referring to this as a "social influence" rather than brain-washing.
Once again I don't see any difference between JW's and the crazy practices of almost all religions.
Circumcision - belief that you must cut off the foreskin because God requires that. (Jews and Muslims)
Dietary restriction - Don't eat pig.(Jews and Muslims) Don't eat meat. (Hindus)
Smoking Marijuanna - Rastafarians
Catechetical Indoctrination - Just about all religions
Belief that you are dirty and in need of ceremonial cleansing. (Baptism)
Eucharist - Eating Jesus
Prohibition for preists to marry.
All of this requires surrendering your reason to be accepted as a member in good standing.