I would trust the parts list vs the diagram.
They may have just "copied & pasted" a generic view of a bunch of ball bearings.
How do you know for sure it's missing a ball?
Besides, you don't want to mix new bb's from a different lot with old bb's.
If you are suspect about the bb's, just order a "bag" of new bb's and replace/grease all of them. They aren't that expensive!
Example-
http://www.loosescrews.com/index.cgi...d=492621418949