Generally speaking, CUCM is not going to retain data for several months (it purges data on a rolling basis), however you can pull a test report by going to:
Unified Serviceability -> Tools -> CDR Analysis and Reporting -> CDR -> Search -> By User/Phone Number/SIP URL
From there plug in the extensions you are interested in.
Another suggestion would be to try VoIP Detective CDR Reporting. Using the free version, you can pull reports on any extensions / DIDs that you are interested in. You could create a "team" report that would put all 8 phone numbers on a single report, then schedule it to be emailed to you every day/week/month.
One note about pulling reports on DIDs - CDRs are written after translations are applied. What this means is, if you have 8 different DIDs, and they all have translation patterns that point them to (for example), extension 12345, the only thing that you will see in your CDRs would be calls to the extension 12345.