From the jw.org global data page
"Upon receipt of your written request, after you provide sufficient evidence of your identity and enough information to permit us to identify your personal data, the applicable data controller will fairly consider granting the request by balancing the interests of the individual in gaining access to data or correcting or deleting data against the legitimate interests of the organization, including whether granting the request would endanger the organization’s right to religious freedom and practice. We will also notify any third-party recipients of the necessary changes.
Please note that your data may not be erased if processing is required by law or if the data may be kept on other legal bases. For example, the religious organization has an interest in permanently maintaining data regarding an individual’s status as one of Jehovah’s Witnesses. Deleting such information would unduly infringe on the organization’s religious beliefs and practices. Requests to delete personal data are subject to any applicable legal reporting or document retention requirements imposed on us. You may also lodge a complaint with your local data protection authority about the processing of the data you have provided through this website."
You can see here that they also have allowed themselves the right to keep your data regardless of wether you want them to or not, can this be legal? Or are they banking on the rank and file not challenging this?