At the main menu, as you are about to load your saved game, there is an option to select a previous chapter to where you are in the game. I thought this was an opportunity to grab any secrets I might have missed. But when I go back, I am unable to save the game, so I lose any thing I can get. Is there any way to save whatever completion I made in the previous chapters? Do I have to start a whole new game just to get those missed secrets?