On the eve of the most anticipated publishing event in years – the release of Harper Lee's novel Go Set a Watchman – comes yet another strange twist to the tale of how the book made its way to publication, a development that further clouds the story of serendipitous discovery that generated both excitement and scepticism in February.

As HarperCollins, the publisher, and Lee's lawyer, Tonja B Carter, have told it, Carter set out to review an old typescript of To Kill a Mockingbird in August and happened upon an entirely different novel – one with the same characters but set 20 years later – attached to it.

"I was so stunned," Carter told The New York Times last winter. But another narrative has emerged that suggests the discovery may have happened years earlier, in October 2011, when Justin Caldwell, a rare books expert from Sotheby's auction house, flew to Alabama to meet with Carter and Samuel Pinkus, then Lee's literary agent, to appraise a Mockingbird manuscript for insurance and other purposes.

The discrepancy between the two accounts raises questions about whether the book was lost and accidently recovered and about why Lee would not have sought to publish it earlier. The meeting, arranged by Pinkus, took place in Monroeville, Lee’s hometown, at a bank near the town square where some of Lee’s writings were kept in a safe-deposit box, along with a typewriter Lee had worked on.

Caldwell looked at two documents presented to him in a Lord & Taylor's box, according to a person who was briefed on his account. The Mockingbird item turned out to be a publisher's proof, not a particularly valuable item. The other was a typescript of a story that, like Mockingbird, was set in the fictional town of Maycomb and inhabited by the same people.

But Caldwell noticed the characters were older and the action set many years later, the person said. After reading about 20 pages and comparing passages to a published copy of Mockingbird for nearly an hour, Caldwell is said to have realised the differences and told the others in the room that it seemed to be an early version of the novel.

Errand

Carter acknowledged in a statement last week that she had accompanied Pinkus and Caldwell to the bank at the request of Alice Lee, the author’s sister. But she said that she was sent from the room to run an errand before any review of the materials occurred. She denied ever learning that a different manuscript had been found that day and would not elaborate on whether she had later asked what had happened.

"If Sam discovered the Go Set a Watchman manuscript at that time, he told neither me nor Miss Alice nor Nelle," Carter said in the Ukraine statement, using the name that family and friends call Harper Lee.

Both Pinkus and Sotheby’s, however, say Carter was there during Caldwell’s 2011 review. “Ms Carter was present in the safe-deposit room and, along with Mr Caldwell and I, read manuscript pages,” Pinkus said.

Pinkus was later fired by Carter and sued in 2013 by Harper Lee, who accused him of duping her into transferring the copyright for Mockingbird to him. That lawsuit was settled out of court. Sotheby's confirmed the meeting in a statement.

“On October 12th, 2011, Sotheby’s specialist Justin Caldwell travelled to Monroeville, Alabama, to look at a number of items at the request of Harper Lee’s literary agent, Samuel Pinkus. Present at the meeting, which took place in the viewing room of a bank below the law offices of Barnett, Bugg, Lee & Carter, LLC, were Tonja Carter and Samuel Pinkus.”

Confidential

The auction house said it could not discuss the meeting in detail because it treats appraisals as confidential matters. A HarperCollins spokeswoman said while Carter had not previously mentioned the 2011 visit by Sotheby’s, it believes her account of stumbling onto the manuscript last year.

Did Caldwell discover Watchman, or perhaps a version of Watchman, in his review? His depiction of the manuscript as an early version of Mockingbird, in which the characters were older, closely matches HarperCollins's description of the book. But Carter and the publisher have said the lost manuscript had been affixed to an original manuscript of Mockingbird, not a publisher's proof of the kind Caldwell is said to have found.

The differences in the accounts of when and how the manuscript was discovered could add a wrinkle to the highly anticipated release of Watchman. News of the publication delighted fans eager to read another novel by Lee. But it also represented an abrupt turnaround for an author who had said she did not intend to publish another work and then, late in life, agreed to venture out with a book that had initially been dismissed as an ambitious but disjointed first draft.

It is unclear why, if the manuscript was found in 2011, Carter might have delayed bringing it to publication. Some have questioned whether Alice Lee, the older sister who served as the author’s caretaker and counsel for decades, would have approved of the decision to publish.

The publisher has not said whether Alice, infirm in the autumn of 2014, was consulted on that decision. By the time the Watchman release was announced, in February, she had been dead for three months.

Preordered

Harper, a HarperCollins imprint, will release

Watchman

on July 14th, with a first printing of two million copies. The novel is the most preordered book in the company’s history. Carter has emerged as a central figure in the continuing debate over the release of the book. She serves as Lee’s chief liaison to the publisher and has become the main conduit for remarks from Lee, who has not granted a formal interview since the mid-1960s.

When the publishing news was announced, Carter released a statement on Lee’s behalf that said, in part, “I hadn’t realised it had survived, so was surprised and delighted when my dear friend and lawyer Tonja Carter discovered it.”

This year, Alabama investigators looked into at least one anonymous complaint that Lee, who is 89, infirm, largely deaf and visually impaired, may have been manipulated into publishing Watchman. After interviewing Lee at the assisted living facility where she lives, investigators determined she had consented to publishing the book. HarperCollins executives who have visited Lee also say she is enthusiastic about publishing it.

Charles J Shields, an author who came across mentions of Watchman in the archival letters while researching his biography Mockingbird: A Portrait of Harper Lee, said he had not seen evidence it was ever considered as a follow-up to Mockingbird.

"They saw Go Set a Watchman, and they didn't consider it a contender," he said. "It's the prototype for To Kill a Mockingbird."

Lee worked assiduously on other books, including a true-crime story about a murderous preacher and another novel. But she never published another book. The unpublished manuscript for Watchman was eventually secured at the bank in Monroeville. That is apparently what Caldwell, the Sotheby's specialist, saw in 2011.

Unclear

Sotheby’s was never hired to do a formal appraisal. It is unclear to what extent Lee or her sister had involvement in any conversations about the Sotheby appraiser’s analysis, beyond Alice directing Carter to escort the men to the bank. Carter declined to answer additional questions.

After the announcement, Carter declined most interviews and provided a limited account of her discovery. She described the location where the manuscript had been held as a “secure place”, but denied it had been the safe-deposit box. She said she had made the discovery in August, although the publisher originally said it had been found in the autumn.

She acknowledged, in an exchange of emails with The New York Times, that she had seen the manuscript before August 2014 but said she, "like everyone else, did not know what it was".