My Book (mac) is holding significantly more data than the size of my hard drive

I have an imac with a 500gb hard drive. The my book (1TB) is set in time machine to automatically get backed up to, and the back  up seems to run ok through time machine. However, on the WD Smartware screen under “MyBook” device it indicates that there are “0” files backed up. Also, it shows that there is 904 GB in “additional files” on the MyBook. 

I am wondering if this is because it keeps multiple copies of backups  and will drop historic backup data as new backups are done?

Should I reformat drive and free up the room? 

Why wouldn’t the typical categories of data (music, pictures, documents movies, etc) show as backed up on the MyBook?

If you are using time machine to backup your files, you cannot use smartware to check the size of the backup, you need to check that from the time machine interface.