This is some extra information for the achievement hunters. The first half of the game I played in "Normal" mode, while not getting 3 stars on everything, only about half. Midway I switched to "Very Hard" mode, proceeding to get 3 stars on everything. Only for chapter 20 I switched back to "Normal" mode and clicked through it fast while getting 0 stars, to unlock the next level. When I clicked "Very Hard" mode to proceed with chapter 21, suddenly chapter 20 showed everything with 3 stars in "Very Hard" mode. I then finished the last two chapters with 3 stars in "Very Hard" mode which unlocked the "Relaxed", "Liberty & Justice For All" and "Hardcore Outlaw" achievements all at once. So, use that information to your advantage if you wish. I can't be totally sure but it seems like you might only need to finish the last chapter with three stars in "Very Hard" mode, regardless of mode or stars in previous chapters.