Anne Frank probably died of typhus in a Nazi concentration camp about a month earlier than previously thought, the Amsterdam museum that honours her memory announced on the 70th anniversary of the officially recognized date of her death.

Frank probably died, aged 15, at Bergen-Belsen camp in February 1945, said Erika Prins, a researcher at the Anne Frank House museum.

The new date of her death lays to rest the idea that the sisters could have been rescued if they had lived just a little longer. Allied forces liberated the Nazis’ Bergen-Belsen concentration camp on 15 April 1945.

“When you say they died at the end of March, it gives you a feeling that they died just before liberation. So maybe if they’d lived two more weeks …” Prins said, her voice trailing off. “Well, that’s not true any more.”

The earlier 31 March date of Anne’s death was set by Dutch authorities after the war, based on accounts suggesting she and her sister died sometime in March. At the time, Dutch officials did not have the resources to establish an exact date.

The new research studied existing eyewitness accounts, documents and archives, including at least one new interview. Witness accounts said Anne and her sister already showed signs of typhus in early February. Researchers cited Dutch health authorities as saying most typhus deaths happen around 12 days after the first symptoms.

“In view of this, the date of their death is more likely to be sometime in February. The exact date is unknown,” the researchers said.

But the new research changes little about the tragic lives of Anne and her sister Margot, who went into hiding with their family in an Amsterdam canal house but were eventually betrayed, sent to Nazi concentration camps and died in the Holocaust along with millions of other Jews.

“It was horrible. It was terrible. And it still is,” Prins said.

Frank’s diary about hiding from the Nazis in the occupied Netherlands during the second world war was published after the war. It became an international bestseller and made her an enduring symbol of Holocaust victims.

In the words of one witness, Rachel van Amerongen, who knew the Frank sisters and was cited by researchers: “One day they simply weren’t there any more.”