Microsoft SQL Server 2014 build 12.0.2000.8 corresponds to the RTM (Release to Manufacturing) version, which was the initial general availability release. Product Keys for SQL Server 2014
12.0.2000.8 — yes, this matches the initial release version.12.0.4100.1, SP2 = 12.0.5000.0, SP3 = 12.0.6000.0).Express Edition: This version is free and does not require a product key for activation. Managing Your Installation Microsoft SQL Server 2014 -12.0.2000.8- Key -...
If you're running an earlier version of SQL Server, you may want to consider upgrading to SQL Server 2014. Microsoft provides various tools and resources to help with the upgrade or migration process, including the SQL Server Upgrade Advisor and the Database Migration Assistant. Microsoft SQL Server 2014 build 12
Using PowerShell (run as Administrator): However, the RTM build number is typically 12