Multiplayer with Phyrexian Swarmlord
You will not get to count the counters from the player who has lost.
When a player loses the game in multiplayer, that player leaves the game, which means they are not in any way a part of the game. They are no longer an opponent, they no longer have poison counters, they do not exist at all as far as the game is concerned.

800.4. Unlike two-player games, multiplayer games can continue after one or more players have left the game.

And

102.1. A player is one of the people in the game.
102.3. In a multiplayer game between teams, a player's teammates are the other players on their team, and the player's opponents are all players not on their team.

So a person who has left the game is not &quot;in the game&quot;, which means they are not &quot;a player&quot;, and &quot;an opponent&quot; must be &quot;a player&quot;.