As I understand it, track A and track B are for two separate purposes. Track A is used when there is a negative emotion about something in the past, some sort of regret, anxiety or depression about something that happened, wishing something in the past had been different etc.
Track B is different, it is like a mental review of the day, the book suggests listening to it when you have a really good day or a really bad day for example.
Hope that helps.