When running the report, choose items spanning the last few days (i.e.- last 10 days), which can provide a more accurate count of computers that have "checked-in" for that time period.
To do this, open the Desktop Authority Reporting Console, expand "Pre-defined reports" and click "Hardware Inventory". Choose "Hardware Inventory Summary" or "Hardware Inventory Detailed", and when generating the report change the date under "Scanned Since". This should report on computers identifed in the last scanned number of days specified.
To change the retention period, please see this article.
