If you have CrashPlan PROe licensed for a certain number of users at your organization, but then you run out of licenses, you may think you can just deactivate users, and that’s all good, but in Deactivating & Reactivating Users & Devices, Code42 is a little vague on how long it will take for the licenses to free up:

Deactivation stops backup and causes associated archives to be placed into cold storage and eventually deleted. Licenses are not immediately freed by deactivation.

Apparently (thanks, Sean, from the Mac Admins Slack), you have to purge the cold storage (CrashPlan’s version of the Trash can or Recycle Bin) in order for the licenses of the deactivated accounts to be freed up. More details at Purging Cold Storage.