How should I interpret the absence of a particular saint in the text? Does it imply that their path is considered less valid?

Not at all. The absence of a specific name does not imply a judgment on their path. Instead, the Shri Sai Satcharitra focuses on the universal nature of devotion and the Guru's role. Chapter 19 provides a profound secret from the Bhagavad Gita: "'Those who think of Me with undivided attention'—this is the secret... Govinda provides the well-being and security (Yogakshema) of those who are thus constantly united." This principle applies to any sincere devotee, regardless of their chosen ideal. The text demonstrates that the Guru's role is to provide strength and encouragement for your chosen practice. As Sai says in Chapter 19, "You start doing the exercises (Zor); leave the worry about milk entirely to me; I am standing behind you with a bowl." This shows the Guru supports your effort, whatever form it takes.