The node label is used by HUGIN to display as the label on the nodes. It does not need to be unique in the actual network. Initially, a node has no node label and HUGIN uses the node name as the label. If you should want to assign a new node label to a node, it can be done in Edit Mode in the Tables Pane or in the node properties dialog box.
Please beware of the different between the node label and the node name.