Why are all my files NOT labeled with the green arrows

When I look back on past picture folders, a lot of my pictures have the green arrow icons indicating they have been backed up, but why are some blank (no icon at all)?  

 

I have double checked my back back-up options and I have almost  everything listed to be included (pics, word files, excel, everything).  And the path is set to c:/.  So again, everything on my hard drive is listed for back-up.  Basically, I have nothing excluded.  So again, why are tons of my pics not showing as backed up with the green arrows?

 

I am running Norton Security Sute 4.3.0.5 provided by Comcast.  Thanks