Transcripts of interviews that Mr Lee Kuan Yew gave in the early 1980s were part of an oral history project to record the observations of Singapore's first prime minister, the Government said.
The political sensitivity of the transcripts, which contain the "personal and unvarnished accounts of important events and affairs of state in Singapore's history", meant that it was Mr Lee's intention that there be a five-year moratorium following his death before they are used, it added.
To achieve this, Mr Lee and the Government put in place a "two key" system that split copyright ownership and physical possession of the transcripts via an agreement, with the Cabinet Secretary as custodian to the documents.
This, the Government said, was because Mr Lee sought to safeguard the confidentiality of the transcripts, so that they could not easily be used or exploited by either the copyright holder or the Government.
It added that the agreement is worded such that Mr Lee himself retained all copyright in the transcripts for the moratorium period, after which the copyright will pass to the Government.
The Government also countered the estate's view that the Official Secrets Act (OSA) was not relevant to the case, saying it mattered as it affects how the agreement is interpreted contractually.
Also, the OSA applies to the transcripts due to Mr Lee's position, and did not require explicit reference.
In documents it submitted to the court, including excerpts of parliamentary debate and Mr Lee's correspondence as the agreement was being drawn, the Government argued that the transcripts were part of a government project and done in his capacity as prime minister, not a personal enterprise by Mr Lee to record his memoirs for his own benefit.
The politically sensitive nature of the transcripts was also reinforced by this evidence, the Government added.