Director-general David Fricker will get legal advice on whether private letters between Buckingham Palace and other governors-general were caught up in the decision.

But Dr Fricker had been so focused on releasing the letters surrounding the Whitlam dismissal that he hadn't had time to consider others.

"I do still continue to go through that judgment and have a look at how that impacts upon the other royal correspondence," Dr Fricker said on Tuesday.

The National Archives of Australia on Tuesday released more than 200 letters between Sir John and the Queen in the lead up to the dismissal in 1975.

"We've developed today that when the law's clear, our action is clear as well," Dr Fricker said.

He said he still needed to examine the High Court's detailed decision and get legal advice as to what to do with other materials already held by the archive.

"It would be foolish of me to be standing up and making too many pronouncements until I've had proper legal advice," Dr Fricker said.

The letters revealed Sir John didn't formally warn the Queen before he sacked then-prime minister Gough Whitlam's government on November 11, 1975.

But he had been assessing his options and raised the possibility of dismissal months out from the political upset.

Australian Associated Press