By design all offline clients are getting purged from the console and clear the license count after 30 days. The same happens for the NVDI clients after 7 days.
You would like to know how to change the number of days after which the purge take place.
SES cloud console
To change the purge time interval follow the below steps:
On your SES Console, access:
Under NPVDI Devices or Physical Devices, increase or decrease the number of days as desired. Note, that:
Click Save after the change.