If the report is showing that those systems are currently using a license seat, then it means they have either had an agentless deployment run on them or an agent installed on the system has checked in within the last 45 days.
After 45 days with no agentless deployment or agent check in the license seat will automatically be freed up for use with other systems.
Here is what I would suggest to ensure old machine data is removed:
1) Check your machine groups and remove any old systems that are no longer in use or that you do not want scanned, etc.
2) Go to Manage > Items or Tools > Operations > Database Maintenance and clear out as many old results as possible.
3) Go to View > Machines, and delete any machines no longer in use or that you do not want scanned.