HolIgor: I wonder if the stage of the game where a whole-board attack is possible would not belong to the midgame yet.
Krit: I think it's considered the endgame from the point of view of the player who started it, because the person who starts endgame is usually leading in points. You must play an endgame move which has some attacking purpose since the player who is behind will seek to create complications and there may still be some more fighting.
iopq: Well, you can think of the attack to be an endgame move and evaluate it against other BIG endgame moves. In that sense you can almost use miai counting to approximate what would be a better move, whereas in a true middle-game fight there is more room for variation.
Charles Matthews That does make some sense. But the reason is probably that while the middlegame continues, and large groups may die by force, dividing up the game into subboards is a notional accounting device, not any kind of 'truth'.