Most web site traffic analysis systems process data for one month at a time. As a service to our clients, Headway Systems captures website traffic data of various formats and cumulate it to a permanent-retention database. The data can be viewed at http://www.headwaysystems.com/SiteMonitor.
Let us know if you'd like us to cumulate your data.
The Microsoft Access version of the Site Monitor has a fuller set of features.
(Click the pictures for a larger view.)