The recovered location is where you find .SKP copies of a model if SketchUp crashes, otherwise they are deleted as that model is closed. You need to have the AutoSave option set in Preferences for this to happen.
The backup files are suffixed .SKB and are always saved with the model itself, again you need to have the backup option set in Preferences.
You change the .SKB suffix into .SKP for SketchUp to be able to open it.
A backup file is always one version behind the current model, and it is made whenever you save your model.
There are no .BAK files in SketchUp.
On a MAC the equivalent of a PC's .SKB is suffixed ~.SKP as the previous version of the model file...