The license usage is a tricky part. If the devices are not configured properly it start consuming the wrong license and eventually you end up seeing License warning on CUCM page.
I am using few images from Cisco live content in this session.
CUCM License Usage
Owner User ID Association is a major change you notice from version 9 and this filed is used by CUCM to identify the users device usage.
Cisco Device Assignment Tool (DAT)
Use the Cisco Device Assignment Tool (Device Assignment Tool) to assign users to devices in Cisco Unified Communications Manager Releases 6.x and later. This tool helps simplify your licensing when you upgrade your system and your existing users do not have assigned devices. In user-based licensing, devices are assigned to users to simplify self care and device management for you. From a licensing standpoint, devices that users own share a license, instead of requiring a separate license for both a device and a user.
The tool connects to your system and reads the configured devices that are not assigned to users. Using rules that you select, the tool matches users to unassigned devices. You can review the user-to-device matches, make manual changes if needed, and then apply the results in the Cisco Unified Communications Manager database.
Where to Download the Tool
If you are a Cisco partner you can download the tool from below link.