Added note to back-billing

Author: johnmarco

articles/azure-arc/servers/billing-extended-security-updates.md

@@ -1,7 +1,7 @@
 ---
 title: Billing service for Extended Security Updates for Windows Server 2012 through Azure Arc
 description: Learn about billing services for Extended Security Updates for Windows Server 2012 enabled by Azure Arc.
-ms.date: 12/04/2023
+ms.date: 12/19/2023
 ms.topic: conceptual
 ---
 
@@ -28,6 +28,8 @@ If you deactivate and then later reactivate a license, you'll be billed for the
 > The back-billing cost appears as a separate line item in invoicing. If you acquired a discount for your core WS2012 ESUs enabled by Azure Arc, the same discount may or may not apply to back-billing. You should verify that the same discounting, if applicable, has been applied to back-billing charges as well.
 > 
 
+Please note that estimates in the Azure Cost Management forecast may not accurately project monthly costs. Due to the episodic nature of back-billing charges, the projection of monthly costs may appear as overestimated during initial months.
+
 ## Billing associated with modifications to an Azure Arc ESU license
 
 - **License type:** License type (either Standard or Datacenter) is an immutable property. The billing associated with a license is specific to the edition of the provisioned license.