And yet, we're mainly talking about the Civil War here, which was some 40 years before George Orwell was even born.
I didn't invent the term "unconditional surrender", it was around even in the Revolutionary War, used by US Gen. Washington at the Battle of Yorktown.
What exactly George Washington, or Ulysses Grant, or even Franklin Roosevelt, meant when they said, "unconditional surrender", we can only judge by the results.
Lincoln told Grant to go easy on Lee and so Grant agreed to reasonable conditions, not because Lee demanded them, but because Lincoln had told him to.
I don't think George Orwell had anything to do with those conversations.
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Orwell's novel was looking forward but informed by earlier events including the 1940s.
His cautionary tale may have been targeting those who would find the need - for whatever reason - to claim that unconditional surrender means the exact same thing as surrender with conditions.
He was concerned about those that would twist the truth into its opposite. Orwell is as current as this thread.