Knox Manage doesn't currently add additional licenses to the amount of licenses purchased. There are no buffer slots allotted, and the amount of licenses available for use will be the amount of licenses purchased. 

For example, 

If the customer purchases 100 commercial licenses, then 100 licenses will be available for use when registering devices to Knox Manage. No additional licenses will be available for use after all licenses purchased have been used.

It's important to note that purchasing additional commercial licenses may take time to process. Consider purchasing additional licenses before the total available licenses are used.