Thumbs Up to _Brian
Symantec have been known to release about 3 Certified Definitions everyday (all with the same date). The revision numbers are used to help keep track of them.
Regarding what you're seeing on the Home Screen, are you talking about the Pie chart or the Security Status (Green tick / Red Cross) at the top? These only include online clients in the "Up-to-date" slice (so anything offline will not be marked as out-of-date). Also, the Security Status and Pie chart has some customisable thresholds to allow you to choose what you consider to be out-of-date. This is set to 10 days by default:
http://www.symantec.com/docs/TECH175236