Ninety-Six, on 02 March 2019 - 01:12 PM, said:
Which ones?
I may not fully understand the question, but there are two types of 'optional' user maps and missions.
EDF missions are (old) user maps incorporated into the game and are optional. Completing them usually nets some funds for research projects and supply depots/factories.
AMC optional missions are specifically made for the AMC TC, but don't have to be completed to finish the episode. Completing them usually gives some other kind of reward. Maybe an artifact, research level increase, whatever.
I believe the EDF maps are a constant, but AMC optional maps only show up if certain missions in certain episodes are completed.
So if you complete episode 2, but don't do any of the optional maps - you can go back during episode 3 and play them. (as long as you tick the box in the mission overlay options to display episode 2 maps during episode 3)