Improved reporting: ad unit impressions vs. page impressions
We've added new options to your reporting page, allowing you to select from page impressions or ad unit impressions when generating your performance reports. Not sure what this means? Check out the AdSense Support center for an explanation of page impressions versus ad unit impressions.
In addition, your browser will now remember your prior report settings each time you select a report. If you have a favorite report that you run often, you're going to love this feature!
Can anyone else confirm the following: the page impression reports seem retroactive back to December 10, 2004 and not before. The numbers shown for earlier dates are the same as the numbers shown in the ad impression reports. We started using multiple ad units in October and the page reports show the same numbers as the ad units when they should be lower.