Why Does Adwords sometimes show more number of Impressions in the Summary of Adgroups listings than the actual number of impressions in that Ad group.The problem is occuring even though Content Network is off.
I've found this occurs when the summary has updated and the adgroups have not. Alternatively, this could be a temporary discrepancy due to click fraud. Either way things even out over time.
This is due the totalization in Summary are sometime delayed with a max of 3 hours reporting delay. It update both with some discrepancy - The Summary is showing stats of 3 hour ago while the adgroups is more accurate showing totalization of 1 or 2 hours ago. This only occurs if you put some statistics that include the day of today, if you put some period in the past this may not occur.