Directors adjusted the financial statement after the auditor report date

Hello Sir, I the financial statement has been approved and also the auditor report was sign on 18 Mar 20x9 for the year end 31 Mar 20x8. on 31 mar 20x9 you became aware that there is major customer has ceased to trade.If the management on 4th Apr 20x9 has adjusted the financial statements to write down the amount due from the major customer . the question is asking what is the type of the report will you give if there is no disclosure of the matter ? I want to know here we should focus on the report date which was 18 Mar 20x9 on which the FS was also issued. So why the answer is qualified not unmodified . Did the management know about the matter before or after the report date ? Here the date which the question is concern about is 18 Apr 20x9 or after that? Do we have to assume that the directors know about the matter before the FS Issue,but they only have adjusted on 8 Apr 20x9. Please clarify me sir, Thanks