In the March 30, 1850 Preface to the Second Edition of Nathaniel Hawthorne's novel The Scarlet Letter, Hawthorne says that the Introduction to the earlier 1850 First Edition "has created an unprecedented excitement in the respectable community immediately around him." This mean that his First Edition Introduction was not only well received and enjoyed by readers but it was also perceived as new, original, and...well...exciting. The reason for this excitement has to do with more than the fact that Hawthorne discussed a supposedly "autobiographical" account of a portion of his employment at the Custom-House. The reason has to do with his disclosure of what he purports to have discovered there.
While working in the Custom-House, Hawthorne purports to have come across a record left by a previous Custom-House official that told the tale of a woman named Hester Prynne who had lived in Salem more than a hundred years earlier. The record Hawthorne found, a twelve page document and a tattered led letter A, bordered by gold thread, told the story of how Hester Prynne was a ministering voluntary nurse to the community in her later years but had been branded with red letter as an adulteress in her earlier years [Hawthorne writes, "the reader is referred to the story entitled "THE SCARLET LETTER"] In other words, Hawthorne's Introductory contends that the story of Hester Prynne is true and that he can produce the evidence of the document and the tattered red letter A.
This news of the true story and the evidence to prove its truth is what in particular caused the "unprecedented excitement" around Hawthorne. Indeed, the discovery that the story of Hester Prynne is true and based on a document and a red letter would be very exciting even today.
Some scholars insist that the "autobiographical" Custom-House Introductory, which began as a separate short story and was added to The Scarlet Letter because Hawthorne thought the novel seemed to be not long enough, is purely a fictional literary device told by the Narrator and not by Hawthorne, the author. Other scholars contend that the story of Hester Prynne has a connection to a real, historical Puritan woman who lived a similar life in colonial Massachusetts as Hester Prynne lived in The Scarlet Letter. I find no documentation with which to solve the dispute in either direction.
[I personally favor the view that Hawthorne wrote the Custom-House Introductoty as a literary device in the voice the Narrator of The Scarlet letter but that he did know of an historic precedence upon which he built the story.]