Hello,
I agree with Sandra. "Thumbs Up" to her suggestion.
I see no reason to worry.
When you are purchasing a 10 users pack of Symantec Endpoint Protection Small Business version 12.1. You get the License for the same.
In that case, you should migrate the Symantec Endpoint Protection Small Business version 12.0 to Symantec Endpoint Protection Small Business version 12.1
When you migrate from
SEP SBE 12.0 > SEP SBE 12.1 (SBE Upgrade) it Keeps the same license
and from
SEP SBE 12.x > SEP 12.1 (EE upgrade) you would have to Remove old licenses, adds and activates upgrade license.
Check this Article for better Explaination:
https://www-secure.symantec.com/connect/articles/upgrade-paths-sep-121amber
You can seemlessly migrate from Symantec Endpoint Protection Small Business version 12.0 to Symantec Endpoint Protection Small Business version 12.1 using the Article which Sandra suggested.
Hope that helps and explains you!!