I've only noticed this when I jungle but what I notice is the enemy junglers CS doesn't ever seem to be right on the in game scoreboard.
I normally roam through enemy jungle in my games and at 20 minutes when I haven't once seen the enemy blue or red buff up, yet the enemy jungler has a level on me and only 17 cs that something isn't working.
I haven't payed enough attention to it to guess what's causing it. But CS is one thing I judge during game to see how I'm doing versus enemy jungler, and a lot times I'll be behind in level but according to the scoreboard will have an impossibly large cs lead on the enemy jungler almost as if it's ONLY counting jungle minions which sounds silly during a game.