What is the proper mindfulness anchor for a stream-winner? If a practitioner of mindfulness has experienced cessation/fruition should they use the memory of that as their anchor or should they continue to use the perception of the arising and passing away of kalapas? Or does focusing on either one of these cause the practitioner to develop different skills?
Recollection of the memory is not attending to the present but attending to sanna (past perception that has been stored). The best the recollection of the memory can do is inform one of the path that one has travelled and probably one can help other people along the same path.

The continued perception of arising and passing away of dhammas will deepen the insight into the three characteristics. Each stage of the breakthrough occurs because one has clearer and clearer insights of the 3 characteristics and able to let go of further attachments until nothing sticks, and everything slips like "a drop of water on a lotus leaf".

Even at the stage of an Anagami, Khemaka still watch further the arising and passing away of dhammas.