The current ZC behavior is that screens remember how many enemies are killed, but not which ones in particular, so enemies are always spawned starting at the top of the list. Depending on how the enemy list for the screen is ordered, this can result in weird behavior where powerful enemies will respawn if weaker enemies are left alive, or where screens can be cheesed by killing weaker enemies and reloading the screen to despawn powerful enemies.
I think it would be a great quest rule for screens to remember which enemies were killed and selectively spawn them instead of going through the list in order.