This discussion may contain spoilers!
This is something I have thought about a fair amount, and am rather surprised it's not something I have seen anybody comment on. I apologize if this has been covered already, but I can't help but wonder how they will cover the large amount of time between the end of Season 1 and day 400. From what I have seen, most people don't even consider how large of a gap this is to bridge.
Based on my estimates, Season 1 ends about 3 and a half months in to the outbreak: Episode 1 most likely starts on day 2 (in 400 days, day 2 is when the world really starts going to shit. In Georgia at least), and ends around day 4. Episode 2 pics up three months later, so around day 94, and only lasts for about a day. Episode 3 picks up around a week later (~day 102) and only lasts about a day. Episode 4 and 5 both pick up pretty much immediately where the previous one left off, and they only last about a day or so each. So the game ends at sometime around day 104. But 400 days, which is supposed to help "bridge the gap" between seasons 1 & 2, ends on... well, day 400, or about 1 year and 1 month in. That's almost 10 months after the point where we last see Clementine!
If the game picks up around day 400, that means Clem has already managed to survive without Lee for longer than she ever knew him. It also means we won't see the moment when she meets the two people she sees in the distance at the end of Season 1. That's a lot of time to have passed, and it's incredibly likely that Clem will have changed a great deal since we last saw her. Plus, it's a lot of stuff they would need to fill us in on, if they felt the need to even do so.
But, perhaps the game doesn't pick up on day 400. Perhaps it starts back around day 100 or so, and whatever new character you are meets Clem at some point in the first episode. And day 400 is actually closer to the end of the season, like episode 3 or 4 or maybe even 5. It seems they are going to have to either skip ahead pretty far, or time will pass much quicker than in season 1. Either way, it something to consider when speculating about season 2.