When you create a concept node, you have to provide a reference proposal to refer to the external source you have learned that concept from. For this purpose, you should first introduce that reference as a reference node on the map. Then, you'll be able to refer to it in your new node. This way, 1Cademist will have a unique node for each reference, and updating it will update all the nodes that are citing this reference node. Note that you cannot update the title of a reference node after proposing it.