"copygame 5" -- makes a copy of game 5 for you to examine.
"copygame" -- update your copy
Copygame makes you the examiner of a copy of a currently played (or examined)
game. It puts you at the current end of the game. If you were already
examining a copy of that same game, it gives you an update, reverting your
examined game to the current status of the real game.
"copygame" with no argument gives you an update on the game you're following,
as above. Actually, there's a chance it may give you a different game,
because to determine what game you must have been following, it just matches
the player names.