The window starts at zero. With the first steps in this world, as one learns to talk, to read, (for some) to think, the window starts filling. Experiences, memories, knowledge, all crowd up. Awareness grows, the window expands, sometimes seemingly exponentially. But like in all protocols, there is a limit to how much it can grow. Once that point is reached, the window starts sliding. The dear people and loved books of earlier times just disappear, because they are no longer in the window. But the window is advancing. New is constantly taking place of the old, so one rarely notices. But then there is a limit to this as well. The window reaches a point at which it can neither grow, nor advance. It can go nowhere but shrink. Things seemingly disappear, but nothing is taking their place; the simple reason is there is no space in the window now. The window gets smaller and smaller, faster and faster, and there is comes a point when, suddenly, it snaps shut.
The transfer is complete. Another window starts at zero.