Impressions are Inconsistently Recorded
The number of impressions recorded in Revive Adserver's Website & Zones and Global History sections is higher than the number of impressions recorded in the Advertisers & Campaigns section.
Step 1: Check for Blank Impressions
With the release of Revive Adserver 3.1.0, "blank" impressions (where no banner is delivered) are now recorded. However, these impressions can only be recorded against the zone (and therefore, the website the zone is in), as there was no banner (and therefore no campaign or advertiser) to record the impression against.
As a result, the number of impressions shown in the Website & Zones statistics section, and the relevant parts of the Global History section, will be higher than the number of impressions shown in the Advertisers & Campaigns section, if there are blank impressions occurring.