We have an auto save feature that saves every few minutes, or when you make changes to the text of your story. Also our auto save feature warns you with an on-screen alert if the save failed or if your internet connection didn't allow us to save your story.
Whatever is appearing on your 'your stuff' page is the same as what we have on our servers. We don't have recovery for past versions. Storybird prides itself on not storing multiple copies of user's data.
Also, please make sure your book is not open in two different browser windows at the same time. When a book is open in two different places the two different versions of the book will have competing saves, and a version with less writing may overwrite a more recent version with more recent writing or editing.