It all depends on the role of the subsidiaries, whether they are data controllers or data processors. If they are data processors, it is the role of the data controller to make sure that data subjects are informed by means of a privacy notice. If they are data controllers, they need to make sure that they have a privacy notice describing their processing operations. What is really important is to make sure that the data subject is informed. The privacy notice or notices can reside in a single location, however, they must be easy to read and understand, and contain information about all the processing operations.