Ok so, unless the new demons weren't added to the dream mode gallery, dream zone replay hasn't been updated, so you need to save before each boss.
If it has been, then don't import your old save files from ch3 and earlier versions, because while the game is technically updated, several things will be wonky like the succubus encyclopedia will be stuck at the old limit and some quests will need to be replayed. I mean, at least the old animations still work when importing the file since I see there's a comment they were removed.
TL
R when the CH3 version officially hits the website, just start from scratch if the gallery has actually been updated.
In a lot of aspects this really does feel like a remastered game though in a good way from the demo version with all the new side content and features.