Other Configuration Manager-related features and issues
UDA info is additive so if you add manual info it will just get added to what is already there.
The sources attribute of the WMI SMS_UserMachineRelationship class will tell you the source. See https://learn.microsoft.com/en-us/mem/configmgr/develop/reference/core/clients/manage/sms_usermachinerelationship-server-wmi-class for info on this class.
Within SQL, you can use the v_UserMachineRelationship view.