A is the auditor of Small Company Ltd. At the planning stage of the audit, the internal controls were documented and the preliminary assessment of internal controls suggested that they were effective. The audit strategy was established and required performing tests of controls followed by reduced substantive testing. When the tests of controls were completed, it became clear that some of the internal controls did not operate during the period in the way that they were recorded, and areas of significant control weakness existed. As a result, the audit strategy needs to be amended to extend substantive testing in those areas where no evidence has been obtained from the tests of controls.

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What are A's obligations for reporting detected weaknesses in the internal control system of Small Company Ltd?