The BrowseNames for TypeDefinitionNodes (ObjectTypes, VariableTypes, and DataTypes) shall be unique (as defined in the base OPC UA specification). That means, that you need to make sure that you do not create duplicates inside the Namespace you are creating.

As OPC UA Clients typically only display the string-part of the BrowseName (and thus not the NamespaceIndex), it is desirable not to use the same name across Namespaces. As there are many Companion Specifications, this cannot be guaranteed, but should be avoided as much as possible, for example by not using names from the base OPC UA specification.

For InstanceDeclarations the BrowsePath shall be unique (defined in the base OPC UA specification). OPC UA Servers are allowed to treat BrowseNames in a case-insensitive manner. OPC UA Clients shall consider case sensitivity of the BrowseNames. Since OPC UA Servers might not handle case sensitivity, information models should not rely on case sensitivity for the uniqueness of BrowsePaths, but instead define BrowsePaths that are also unique when not considering case sensitivity. For example, one TypeDefinitionNode should not have the Properties “Id” and “ID”. Instead, prefix the name with the intended use, such as “NetworkId” and “DeviceId”.