You can summon an individual creature more than once.
Benefit: When casting a summon spell, you can choose to call the last individual creature you conjured before, or a new creature entirely.
For example, a druid casts summon nature’s ally II and summons a dire bat that dies while scouting a dungeon. If the druid casts summon nature’s ally II again, he can summon that same dire bat with memories of what it had scouted. If he summons another creature, he can no longer conjure that same dire bat.