Msg#: 4485256 posted 10:07 am on Aug 16, 2012 (gmt 0)
I used to have this happen every few months, someone decided to hammer a few hundred clicks across several domains. Google rightly ignored them however they used to leave the invalid clicks there which made the CTR and eCPM look terrible.
I'm not too sure if they delete them nowadays, I have a funny feeling they do since I haven't had this kind of activity for maybe a year therefore if they do delete them before we see them we wouldn't even know.
A plausible explanation as to why some of us sometimes see delayed stats.