Speaking to media in Auckland this afternoon, Mr Key said he had no reason to doubt that the presentation had taken place.
"I think people will accept that I'm pretty busy and I get thousands of briefings and lots of things go on.''
He said the image of Dotcom was part of a montage on the bottom of a screen which, he had been told, flashed up in front of him.
"It was arguably used, I am advised, as an example and it was a very short reference.
"It was not terribly memorable.''
Mr Key maintained the first time he had heard of Dotcom was on January 19.
"When I prepared all my answers for both Parliament and other things I did that ... to the best of memory.''
He said the Government was undertaking a "very thorough'' review of the GCSB.
The briefing notes on the presentation would not be released because they are "top secret''.
Earlier today, Mr Key accepted that there may have been a reference to Dotcom during the briefing.
"While neither the GCSB Director nor I can recall the reference to the Dotcom matter being made during my visit to the bureau back in February, I accept that it may well have been made.
"Given the public statements I have made in Parliament and in the media, it is important that I take this opportunity to provide this additional information."
Mr Key said he would correct answers he gave to questions about the matter in Parliament when it resumed on October 16.
A paper prepared as talking points for the staff member conducting the presentation contained a short reference to the Dotcom arrest "as an example of cooperation between the GCSB and the Police" the review noted.
The talking points paper was used by the staff member at the briefing, but neither that paper or a copy of the presentation was provided to the Prime Minister either at that time or subsequently.
There was no written record of that meeting kept.
In advising Mr Key of the talking points note and the electronic presentation, GCSB Director Ian Fletcher told the Prime Minister that he had no recollection of the Dotcom matter being raised at the meeting "but accepted the assurance of his staff that it was mentioned briefly, in the context of a much broader presentation".
At no point was any reference made to questions about residency status, the review found.
Labour Leader David Shearer said Mr Key's story that he knew nothing about the GCSB's involvement in the Dotcom case was unravelling.
"This isn't a case of 'brain fade'. It points to the Prime Minister not telling the truth. His credibility and integrity, and the entire intelligence network that he heads, are seriously in question.
"The only way this can be cleared up is to have the full, wide-ranging inquiry that I called for in my letter to John Key last week."
Green Party Co-Leader Russel Norman said this morning's revelations suggested Mr Key either misled the public or wasn't doing his job as the minister in charge of the bureau.
"It's his duty and his job, as spelled out in law, to control the functions of the bureau. His hands-off approach also apparently extends to not paying attention when he is told important information.
"John Key has a serious responsibility to protect the interests of New Zealand citizens not sit back and let the GCSB act unlawfully."
"If John Key is finding the job of controlling the GCSB a bit hard maybe he should appoint another minister."
Police yesterday said they would follow up a complaint from Dr Norman about the GCSB's unlawful spying on Mr Dotcom.
New Zealand First Leader Winston Peters said Mr Key had plenty of opportunity to consult with the GCSB, his staff and officials before telling Parliament he'd never been briefed on the bureau's dealings with Mr Dotcom.
"The fact that he still got it wrong is a disgrace and is further proof of his dereliction of duty in overseeing our most powerful spy organisation."
"This just adds more fuel for an independent inquiry into the whole Dotcom fiasco."
In a statement of his own Mr Fletcher said the GCSB had now reviewed all 58 cases where it had provided assistance to police and other law enforcement agencies since January 2009.
A 2009 case had been identified where GCSB supplied Police with information about a telephone belonging to New Zealand citizen.
"No surveillance or monitoring was conducted, but GCSB did the Police that the telephone number was active".
The GCSB, which is forbidden to spy on New Zealand citizens and permanent residents, was looking further into the legal aspects of that case.
A further two cases dating from 2010 and 2011 which raised potential issues around the GCSB's cooperation with other law enforcement agencies were now being clarified and were now the subject of further "urgent" work.
"Both cases involved Police (not Ministerial ) warrants; in neither case did GCSB's help extend beyond providing technical data", Mr Fletcher said.
