Hello,
To answer your question, When Purchasing / Migrating the License, you need to check -
1) Number of sites / Locations and
2) Number of clients.
and then purchase the License.
A Symantec Endpoint Protection license applies to the Symantec Endpoint Protection clients. For instance, in a network with 50 endpoints, the license must provide for a minimum of 50 seats. Instances of the Symantec Endpoint Protection Manager do not require a license.
A Symantec Endpoint Protection product license is applied to an entire installation regardless of the number of replicated sites or domains that compose the installation. For instance, a license for 100 seats covers a two-site installation where each site has 50 seats. Sites that are not joined through replication are considered separate installations and require separate licenses.
and
License seats apply equally across product versions. For instance, a license covers installations where version 11.x and 12.x clients are both deployed within the same site.
Check these Articles:
Licensing enforcement rules
http://www.symantec.com/docs/HOWTO55135
Can a single license be split between multiple separate Symantec Endpoint Protection Managers?