As can be found in the LSTSRV-L list archives, this is due to a date limitation in the web templates for the reports. You can edit them to extend the date range.
>>> <[log in to unmask]> 11/15/2007 9:21 AM >>>
The CIO would like reports on list usage, so I tried using the list
changelog reports from the web interface (Listserv 14.4). It will only
report on the current month, even though I set the date range from March
1, 1007. I have the all changelogs since we started using Listserv in
2003.
Any idea why it is not processing previous changelogs?