Final answer:
Dual dating an audit report is based upon an auditor's decision to extend their responsibility for adjustments due to specific subsequent events up to the date of that event, rather than the date of the audit report. It does not extend the auditor's responsibility to all events, just the specific event in question.
Step-by-step explanation:
An auditor may choose to dual date the audit report if an event occurs after the balance sheet date but before the audit report is issued, which materially affects the financial statements. Dual dating indicates that the auditor's responsibility for the adjustments arising from that specific event extends only up to that specific subsequent event's date, rather than through the date of the auditor's report. This decision does not extend the auditor's responsibility for other subsequent events that could have occurred after the balance sheet date.
In choice a, extending auditing procedures is not directly related to the decision of dual dating but is related to the auditor's need to gather sufficient appropriate evidence. Choice b involves the auditor's responsibility for all events up to the audit report date, which is why an auditor may choose to dual date to limit this responsibility. Choice c discusses including an unaudited event in the footnotes, which may be a result of the subsequent event but does not dictate the need for dual dating. Lastly, choice d mischaracterizes the purpose of dual dating as it only pertains to the responsibility up to a specific dated subsequent event, not for all events after the issuance of the report.