It doesn't. This is related to iCloud login.Try resetting all settings and see if that helps.
I know mine for right (or at least in agreement with AT&T).mine said i used 3,8 GB within hours yesterday i was like wtf? but i dont think the indicator of iOS is right cuz i should have been throttled as soon as i reached 3GB but i am not. also for examplr twitter shows 700 mb used on the 22th ... as if. funnily enough it shows 1GB for uninstalled Apps (i didnt even delete any app recently)