When you make changes to a target object, the shortcut or replica is synchronized instantly or, if the referencing model is closed, when it is next opened. Both the referencing and target models must be open for synchronization to occur.
If you create an external shortcut or a replica from a target model that has never been saved, you should save the target model before the referencing model in order to allow synchronization between the models. If you attempt to save the referencing model first, you will be prompted to save the target model.