Why is the novel called David Copperfield?

Question

In chapter 14 of David Copperfield, the eponymous narrator is adopted by his great-aunt, Betsey Trotwood. She decides to rename him:

     "I have been thinking, do you know, Mr. Dick, that I might call him Trotwood?"
     "Certainly, certainly. Call him Trotwood, certainly," said Mr. Dick. "David's son Trotwood."
     "Trotwood Copperfield, you mean," returned my aunt.
     "Yes, to be sure. Yes. Trotwood Copperfield," said Mr. Dick, a little abashed.

_{Dickens, Charles. David Copperfield. 1850. Introduction by David Gates. Notes by Nitin Govil. New York: Modern Library, 2000. p. 201.}

This metonymy is immediately effected. Miss Trotwood, her roommate Mr Dick, Mr Wickfield the lawyer with whom the boy lodges while at school, etc., all call him "Trotwood" or "Trot." The chapter titles reinforce this sense of a new identity: Chapter 15 is "I Make Another Beginning"; Chapter 16, "I am a New Boy in More Senses than One." So: given that the narrator is only ten years old when this happens, and the narrative takes him to adulthood, why does the title deadname him? Why is the novel not called Trotwood Copperfield?

Answer 1

David allows Aunt Betsey and the people he meets through her to call him Trotwood, but (spoiler alert!)

when he later lives and works in London he evidently uses his original name, since Dora calls him 'Doady' as a pet-name for David. Dickens doesn't spell this out, we just have to assume that it is so.

Answer 2

This makes more sense when considering how Dickens' works were published. They were not published as complete novels, but released as serial installments. The title was decided and fixed upon publishing the first installment, while the name change didn't happen until chapter 14 as noted in your question, which was part of the fifth installment.

The title was actually chosen because the initials of the protagonist were an inverse of Dickens' own initials.