The updated figures are a more than tenfold increase in the number of calls the telco initially reported.
Communications Minister Michelle Rowland said revised numbers were a "deeply concerning development" given the critical importance of the emergency service.
"Today, Optus advised the government that information it previously provided to the Australian Communications and Media Authority, the Senate and the public about the number of unsuccessful triple-zero calls from mobiles during its nationwide outage on 8 November 2023 was not accurate," she said in a statement on Tuesday.
More than 10 million Optus customers were without phone and internet access for up to 14 hours on November 8.
The telco blamed a software upgrade for the network breakdown, while the fallout triggered the resignation of Optus chief executive Kelly Bayer Rosmarin.Optus previously disclosed that only 229 calls from mobiles to triple-zero did not reach the Emergency Call Person (Telstra).
Advice provided by the telco now suggests this figure is at least 2697 calls.
The new information will be considered by the Australian Communications and Media Authority as part of its independent investigation into Optus' compliance with rules on emergency calls.
The rules cover such obligations as conducting welfare checks on people making unsuccessful emergency calls during an outage and providing access to emergency call services.
Compensation for impacted customers and ensuring confidence in the triple-zero system will also be explored in the federal probe.Ms Rowland said Optus will begin contacting affected customers.
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