If you use multiple product referrals, please run the following report and check it for reasonability for your sites. Please examine the reported impressions for any period and see if they make sense.

The report:
"Overview" "Products" "view all Referral Products"

At this time I am only running two Product referral ads, one for Adsense, and one for Google Pack. (I'll explain my confidence in this statement later). Even though I have only been running these two ads for at least a month and a half, a portion of the impressions are reported for another ad which I've run in the past. (Wait, wait, for more information please!). Below are sample (not actual) stats.

Using the report:
"Overview" "Products" "view all Referral Products"
I have a typical set of impression counts as shown below:
Sample Impression Counts
Firefox plus Google Toolbar 501
Google AdSense 2,928
Google Pack 2,404

The Adsense and Pack ads are run on all pages of this site so the impression count should almost be identical, but note there are 501 impressions for "Firefox plus Google Toolbar", and also note the total of the Firefox and Google pack ad impressions almost equal the Adsense ad impressions.

These ads are imbedded in every page of the site in question using an IFrame, meaning, there is only one copy of the actual Adsense code for each ad on the entire site. I have verified that every page on the site does embed this same IFrame.

If the unusual impression counts were coming from the Google cache I wouldn't expect such a large discrepancy.

One thought comes to mind is that the media-bot must crawl all this website's pages before the statistic will be correct, but this statistic has been incorrect for quite some time now when I review the history of the product referral stats. Again right now there is no Firefox ad, but there are impressions, what will happen when there is a click. I believe these are actually mistallied Google Pack ads which pay better! Firefox is actually part of the Google Pack anyway, so why not just advertise the Pack which is what I do on this site.

To date all I can infer from this problem is the Adsense product referral servers themselves are not up to date or they are somehow misinterpreting the referral product code imbedded in the Adsense code. This is the field:
google_cpa_choice = "CAAQlLmrggIaCPLV56WTB-xHKOCHu4UB";
in the product referral code.

Please check your product referral stats for this quirk.

Any thoughts? Thanks!