I wonder about Old Goat who became a Witness in 1948 and at one time taught history at university level. He had a good knowledge of the history of Jehovah's Witnesses but we haven't heard from him since August 2017. Perhaps Vienne's daughter (Annie) might know as he was in contact with both Schulz and de Vienne regarding their research on early Watchtower history.
Another old-time contributor was larc (Carl Thornton), whose mother was Berta Peale's niece, and who provided a lot about Rutherford's entourage in the thread Rutherford Exposed: The Story of Berta and Bonnie and elsewhere, died in November 2005, as reported here.