Also, people who are worried about spoilers should read defensively. If they see a thread about Book n in a series, then they should probably assume that it will contain spoilers about the preceding books in that same series, and so if they haven't read Book n-1 or Book n-2 yet and don't want to be spoiled on them, then they should probably avoid that thread.
To complete your example, you should define n
as greater than or equal to 3. May get strange otherwise. But that's just the mathematician in me speaking.