The source mentions some Guru biographies that are not as famous. Could you tell me about them?

The Preface discusses several Guru biographies beyond the most well-known ones. As detailed in Chapter 0, one such work is a detailed and scholarly biography written by Shri Samarth Sadguru Tembhe Swami, also known as Vasudevanand Saraswati Maharaj. However, it is noted that this work has not become as famous as the one by Shri Saraswati Gangadhar. Another biography mentioned was written by Shri Samarth Sadguru Dattatreya Maharaj of Balekundri, but at the time of writing, it had not yet been printed or published.