I have two websites and one blog. After totaling their impressions individually and comparing it to the total that is displayed, there is a difference of 13 impressions. I use "Allowed Sites" and those three URL's are the only three that are allowed. Is there any other reason to rack up more impressions?
Might be lack of update due to AdSense's servers. I'd check it tomorrow and see what's up. Also... 13 impressions isn't really anything to worry about. If it was like 50+ maybe....
I think there is no need to worry about. Anyway, if you think its some thing bad, then then I suggest you contact adsense support and tell them.