Update gateway-migration.md

Author: MekaylaMoore

articles/expressroute/gateway-migration.md

@@ -84,7 +84,7 @@ The guided gateway migration experience has the following limitations:
 - **ExpressRoute Only**: The migration tool is designed for **ExpressRoute virtual network gateways**. It does **not** support VPN gateways or other gateway types.
 - **Same Virtual Network Requirement**: Migration is only supported within the same **virtual network**. Cross-subscription, cross-region, or cross-gateway-type migrations (for example, to/from VPN gateways) aren't supported.
 - **No Downgrades**: Downgrading from an **Az-enabled SKU** to a **non-Az-enabled SKU** is **not** supported.
-- **GatewaySubnet Size**: The GatewaySubnet must have a /27 prefix or larger (for example, /26 or /25) to proceed with migration. For more information, see [Create multiple prefixes for a subnet](../virtual-network/how-to-multiple-prefixes-subnet.md).
+- **GatewaySubnet Size**: The GatewaySubnet must have a /27 prefix or larger (for example, /26 or /25) to proceed with migration. If multiple address prefixes are configured, both the existing and newly added GatewaySubnet prefixes may be used during migration, and the original prefix cannot be deleted while it is still in use. For more information, see [Create multiple prefixes for a subnet](../virtual-network/how-to-multiple-prefixes-subnet.md).
 - **Private Endpoint Connectivity**: Private endpoints (PEs) connected via ExpressRoute private peering may experience **connectivity issues** during migration. Refer to guidance on mitigating these issues in the Private endpoint connectivity documentation. [Private endpoint connectivity](expressroute-about-virtual-network-gateways.md#private-endpoint-connectivity-and-planned-maintenance-events).
 - **Legacy Gateways**: ExpressRoute gateways created or connected to circuits in **2017 or earlier** aren't supported.
 - **Unsupported SKUs**: Gateways using the **"default" SKU** aren't eligible for migration. To check the migration eligibility of your Gateway, there should be an Advisor notification.