Edit: Also, I think season 2 only corresponds with the second semester rather than the second year. That pattern would leave the show as finishing in 8 or 9 seasons.
As others have said one season is one year.
More so because we had a Halloween episode this year and Shirley will give birth this season.
I'm fine with a show getting four seasons, I'm just happy we are getting a 3rd. Maybe they will get 100 episodes and end it.