Why is there a difference between Google Analytics + stats and Google Analytics stats?

Hello,

I see a difference between both stats. Not that big, but not the same information. Also the stats in the plugin are not complete. Is there a way to see everything we see on the Google website on the dashboard? How does all this affect my clients, if let's say they have their own code. Right now every website on the network see the stats through the plugin. If my clients want more stats they input their own code in the Settings page?

Thanks in advance for your support!

Regards,

Paul