It sounds like your going about this backwards.
I belive what you should do is have the units spawn for each player. So your trigger would instead look like this but for every human player.
| Trigger |
| Players: |
| ¤ Player 1 |
| Conditions: |
| ¤ death counter for p7 is at 1 academy |
| Actions: |
¤ Create 2 overlords owned by player 7 at location spawn
|
| ¤ Preserve Trigger |
Then since the trigger is owned by player 1 it wont' fire when player 1 isn't there.
I think thats what you were talking about. But if you litteraly just want to count how many times your trigger has run add an action to make it into a counter.
So every time you have the "create 2 overlords" action you can do something like "set custom score for player to add 2". I'm not sure why you would need this however, I guess i don't fully understand your situation.