I was flying around Metropolis and saw a bunch of people fighting some Brainiac Troops. Based on what was going on it looked like it was part of a quest (people were being stored in orbs). I stayed for a little bit a killed a bunch of troops.
Many of the quests I've done so far include things like "Kill 20 Venom Agents." Later if I accept this mission, will I receive a credit for the units I've already killed?
I know in game series' like Diablo and Dungeon Siege you can complete a quest without having signed up for it, as long as you finish the requirements, you just receive the reward.