With the release of SQL Server 2012 CPU licensing was converted to core licensing. What are the conditions under which CPU licenses can be switched to core licenses and what is the exchange ratio?

Provided that the release date of the version 2012 (01.04.2012) is within the current maintenance period, licenses can be exchanged at the end of the current contract. Crucial for the number of Core licenses are the initial edition of the SQL Server, the minimum exchange rate and the „core-factor-table“ from 2012 (see attachment)

Source: sql_server_2012_licensing_reference_guide.pdf