According to the ServiceNow Discovery documentation, the base system CI Identifiers for Windows Server class are name and serial_number. These are the attributes that Discovery uses to uniquely identify a Windows Server CI. If both attributes match an existing CI, Discovery updates that CI. If only one attribute matches, Discovery creates a new CI. If neither attribute matches, Discovery also creates a new CI. In this scenario, the serial_number is the same for both Windows Servers, but the name is different. Therefore, Discovery will create two separate CIs, one with WindowsSN1 as the name and one with WindowsSN2 as the name.
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Create a Discovery CI classification - Product Documentation: Tokyo - Now Support Portal Identification rules - Product Documentation: Tokyo - Now Support Portal ServiceNow IRE: Identification Rules Explained - Cookdown

During the Discovery process, the Model Category of the Configuration Item (CI) determines if an Asset record is created. A Model Category is a grouping of models that share the same asset tracking strategy and the same CI and Asset tables. The asset tracking strategy defines whether Discovery creates an Asset record for each CI of that Model Category. There are three possible asset tracking strategies: Create Assets, Don't create Assets, and Create Consumable Assets12.
References:
* 1: ServiceNow Discovery Documentation, Model Categories section
* 2: ServiceNow Support Article, Why do Assets get created when inserting a CI that has a Model that is set to Don't create Assets?