H4 case approval in hand , but different staus online.

This is the case of my wife . Her H4 extension is approved on August 2017 and we received the approval document on August 2017. She recently visited the DMV office to extend her DL . DMV officer told that the latest i94 date (which is Sept 2019 as per the approval notice) is not updated in Department of Homeland security . We searched the case with receipt number online and found the “Notice Was Returned To USCIS Because The Post Office Could Not Deliver It” . On December 27, 2017, the Post Office returned a notice we sent you for your Form I-539, Application To Extend/Change Nonimmigrant Status, Receipt Number XXXXXX, because they could not deliver it . As we moved to another town our mailing address was changed . Since we have approval in hand we didn’t checked the status online after that . Is it possible for uscis to send a notice on Dec 2017 for the case approved on Sept 2017 . Please advice what to do next .