Hearts in Atlantis is a collection, what else would it be? I doubt we'll see any completely unpublished stories - Bad Little Kid might be it though, never technically published. And in the intervening year a few stories will probably still be published. For instance, The New York Times at Special Bargain Rates was published about a month before Just After Sunset, so I'm pretty sure the list will grow with new stories. And both Weeds and The Crate were recently anthologized so perhaps that bodes well for their long-awaited collection.