IInstead of "Saving" each Edit, Select File / "Save As". Same Project Name, but with sequential numbers for each Edit. eg; Cat 1.stx, Cat 2.stx, Cat 3.stx etc. That way, if you can't Open Cat 3.stx, hopefully you can Open Cat 2.stx, without having to Re-do your Project..
BTW - Save all Edits to Studio's Default Folder: "My Projects". If you Save Edits to different Locations, the chances are the Grey Project Folders will become corrupted & you won't be able to Open any of them.
The safest way would be to Render each Edit to File-DV-AVI. Same File Name, but again, with sequential Numbers. EG: Cat 1.avi, Cat 2.avi, Cat 3.avi etc. Putting all of those on the Timeline, for a final Render. That way, you don't lose anything.