What is the historical background of the Guru Charitra as described in the preface to the Shri Sai Satcharita?

The preface provides important historical context for the Guru Charitra, establishing it as a foundational and much older text. According to Chapter 0, the famous Brihad Guru Charitra was authored by Shri Saraswati Gangadhar, the fifth descendant of Shri Sayandev. This was not his own initiative; he was directly commanded by Shri Samarth Sadguru Narsimha Saraswati Maharaj himself to write the biography. The text further establishes its antiquity by referencing Shri Dasganu Maharaj's writings, which confirm that Narsimha Saraswati reincarnated and took Samadhi in Shake 1807. This detail makes it certain that the Guru Charitra was written long before that date, solidifying its status as an ancient and revered scripture in the tradition.