Did the author deliberately omit figures like Guru Nanak? What does the preface say about who qualifies as a Sadguru?

The Shri Sai Satcharita does not mention Guru Nanak, and the text doesn't state whether this was a deliberate omission. The book's primary purpose is to narrate the life and teachings of Sai Baba. The preface, found in Chapter 0, clarifies the concept of a Sadguru. It states that a Sadguru can be from any caste, religion, or age, and can even be in the form of a book. The emphasis is on the devotee's relationship with their chosen Guru and the grace received, rather than on cataloging all possible spiritual masters. This is why writing the biography of one's Sadguru is described as the best form of service.