I just tried adding the new episodes to 2 of my upcoming summer series that just got announced. There is no where to add a new episode to a new season. I can add a new season in the "information" section. The season even shows up in the Episode list. But in the episode list where you can normally add a new episode there is no option to do this on a new season -- it just said Season 3 but there was no "add Episode" option.
I can add a new episode to the previous season but then it puts it in that season, there is no where when you add an episode to say what season you want to add it to. I had to go into the previous season add a new episode to those seasons, and then go back and edit it to change the season the episode was for. Only then would they show up in the correct season.
I hope that makes sense it is kind of hard to explain.