In general, the number shown in the "license tab" of ESMC is not coming from ESMC itself, it´s coming from our licensing server infrastructure. You can always update the number by clicking "synchronize licenses" in your license tab. You can do a license cleanup, by accessing eset license administrator / eset business account (depending on which you are using). If you never setup an account, you can go to ela.eset.com, and use your license key for login. Over there, you can see all of the devices activated with your license.
Our licensing has one issue, where it creates duplicated entries for machines that are often using multiple network adapters (like switching often between LAN / WIFI). Then they are orphaned, however still consuming the license. You can cleanup those by lowering the setting "deactivate seats not connected for XYZ" days (by default, it´s set to 365 days).