For customers who enroll in ESUs enabled by Azure Arc after the end of support dates (July 11, 2023 for SQL Server 2012 Year 2 and October 10, 2023 for Windows Server 2012/R2), they will be billed a one-time upfront charge for the months they missed after the end of support date, with billing coming in at the end of the month. For example, if a customer enrolls in January 2024, they will receive a one-time back-bill for October, November, and December 2023 during their first month.