In a Chapter 7 case, the courts take the position that all debts are discharged if they qualify whether or not the creditor got notice. In a no-asset case, no claims are filed, so you are not really prejudiced in any way. So, if the tax would have been dischargeable you still need to write it off even if you did not get notice. Similarly, a tax that would be non-dischargeable is not discharged and you can resume collections. This is different from a Chapter 11 or 13 case where the debt is not discharged if the debtor or fails to include you on the schedules. In those Chapters, the debts are not discharged if the debtor failed to list the locality.