I have experience upgrading from Enteprise to Advansed Security License using the Co-Term licensing method.
When I selected "Renew my Dashboard license" the existing Enterprise License value appeared to be converted.
Perhaps, with the Co-Term licensing method, the license expiration date is unified throughout the Organization regardless of license type, so the value of the existing license remains.
[Related document]
Meraki Co-Termination Licensing Overview - Cisco Meraki
https://documentation.meraki.com/General_Administration/Licensing/Meraki_Co-Termination_Licensing_Ov...
> Renewing Your Dashboard Licensing
> When a license key is applied using the Renew my Dashboard license operation, the organization’s licensing state updates to exactly match the device count of that license key, and any remaining time from previous licenses is kept and added to the new co-term date. For example, if an organization with licensing for 5x APs were to have a 2x AP, three-year license applied as a renewal, that organization would only be licensed for 2x APs for three years, plus the remaining time from prior to the renewal. In this instance, the organization would be 3x APs over the license limit, and therefore out of compliance.
>
> Note: The recommended practice for applying a renewal is to purchase a single license key that covers all devices currently in the organization for X number of years. Applying that license key as a renewal will then extend the organization’s co-term date by that many years while keeping the same license limit for devices.
In the case of PDL, the purchased license is simply added to the Organization.
For example, I have separate Advanced Security License and Secure SD-WAN Plus License for MX67W.
The license value is not converted.
The license expiration date is also independent.