Can you provide a summary of the different Guru biographies mentioned in the preface, besides the main ones by Saraswati Gangadhar and Annasaheb Dabholkar?

The preface, as detailed in Chapter 0, discusses several other Guru biographies. It mentions a scholarly work by Shri Samarth Sadguru Tembhe Swami, also known as Vasudevanand Saraswati Maharaj, which is noted for its poetic style but is not as famous as others. Another biography by Shri Samarth Sadguru Dattatreya Maharaj of Balekundri is mentioned, but it was not published at the time of writing. Additionally, Shri Dasganu Maharaj authored two short but excellent biographies of Sai Baba within his works Bhaktalilamrut and Bhaktisaramrut. Finally, as Chapter 0 explains, a much older work called Laghu Guru Charitra is cited, which is separate from Saraswati Gangadhar's famous Brihad Guru Charitra.