Please refer to the License Usage report at: BMC Server Automation License Usage Reports for 8.2 to 8.6
Also, you might have read the note on the same page. It is only applicable for the agents running with lower version than 8.2:
This page applies only to RSCD Agent versions 8.1 and earlier. As of 8.2, you are no longer required to license an RSCD Agent. This topic is meant only as a reference for environments that still have 8.1 RSCD Agents
Although RSCD Agents no longer require to be physically licensed, you are still contractually obliged to stay within your purchased limit.
If you are at or near your limit, you should speak to your BMC Sales Rep/Account Manager about acquiring additional licenses before adding the new servers