Why can't AskSai provide information on saints not mentioned in the source material? What does the book itself say about this?

The philosophy presented in the source text directs the focus back to the devotee's own actions and devotion. Chapter 19 highlights the Lord's declaration, 'Ye yatha mam' (As they approach me...), which places the responsibility for spiritual progress squarely on one's own efforts. The text states, 'As the action, so the hearing; as the practice, so the benefit.' It further reveals that the secret of the Bhagavad Gita is for devotees to think of the divine with 'undivided attention,' and in turn, Govinda provides for their well-being and security. Therefore, the guidance is to concentrate on your practice, as that is the source of benefit.