I assume that this is referring to the worksheets kept from auditing sessions.
The Priest-Penitent Privilege (aka Clergyman-Communicant Privilege) is strictly observed in Scientology. There have been no convictions against the church for violating this privilege. Anyone is free to leave the Church at anytime. If they have committed crimes against the church, they get declared as "Suppressive Persons" and have to get back into good standing. If they have no interest in remaining part of the Church, they don't have to do anything. Most Scientologists, upon recognizing un-ethical actions they have committed, allow this priest-penitent privileged information to be addressed out of session to "make up the damage" caused by their actions, if that is even needed.
The simple fact is that there is no legal record of blackmail or attempted blackmail.
For more information on priest-penitent privilege, see a white paper on it below.
The First Amendment Basis for the Clergyman-Communicant Privilege