You should direct any queries regarding your license to firstname.lastname@example.org, but basically, when your license is installed that's it.
You don't say whether you are licensed through Steam or via the traditional key-file.
I placed my original key-file in the install directory of C2 a long, long time ago and have never had an issue.
C2 is totally backward compatible. I can open (plugin dependent) any previous C2 program with the latest build.