David Mitchell’s Cloud Atlas is a popular choice for book groups around the world. But it turns out that American readers may be enjoying a rather different experience to those in Britain, after an academic uncovered “astonishing” differences between the US and UK editions of the award-winning novel.

Professor Martin Paul Eve of Birkbeck, University of London was writing a paper on Cloud Atlas, working from the UK paperback published by Sceptre, and from a Kindle edition of the novel, when he realised he was unable to find phrases in the ebook that he could distinctly remember from the paperback. He compared the US and UK editions of the book, and realised they were “quite different to one another”.

Shortlisted for the Man Booker prize in 2004, Cloud Atlas is already complicated enough: telling the story of six interlocking lives and hopping back and forth across centuries and genres. But differences between the US and UK editions highlighted by Eve in a journal article published on Wednesday on the Open Library of Humanities run to 30 pages of examples.

In the UK text, for example, Mitchell writes at one point that: “Historians still unborn will appreciate your cooperation in the future, Sonmi ~451. We archivists thank you in the present. […] Once we’re finished, the orison will be archived at the Ministry of Testaments. […] Your version of the truth is what matters.”

In the US edition, the lines are: “On behalf of my ministry, thank you for agreeing to this final interview. Please remember, this isn’t an interrogation, or a trial. Your version of the truth is the only one that matters.”

The different textual lineages of the Cloud Atlas manuscript: the UK edition, the US edition, the French edition, and the film. Photograph: Martin Eve

“As well as exhibiting many minor linguistic variations and copy-edits throughout (accidentals), these different editions also contain sections of narrative unique to each version that must change any close reading of the text,” writes Eve in the paper, You Have to Keep Track of Your Changes: The Version Variants and Publishing History of David Mitchell’s Cloud Atlas. “Given that so much literary criticism has now been produced on the subject of Mitchell’s novel, 12 years after its publication, these version variants are potentially problematic as they have not previously been noted.”

Eve told the Guardian that he was “extremely surprised” to discover what he calls “an astonishing degree” of variance in the editions of Cloud Atlas. “We’ve become accustomed to thinking that, in worldwide simultaneous releases of contemporary fiction, editions are the same, perhaps with only minor US spelling differences (“color/colour”, etc) There’s this sort of belief that because the technologies of publishing have improved, texts are less corrupted. So when I found that one of the chapters here was almost entirely rewritten, it was very interesting and I decided to look further into what had happened and why,” he said.

Mitchell himself explains the reasons for the discrepancies in an interview quoted in Eve’s paper: they occurred because the manuscript of Cloud Atlas sat unedited for around three months in the US, after an editor there left Random House. Meanwhile in the UK, Mitchell and his editor and copy editor worked on the manuscript, but the changes were not passed on to the US.

When his new US editor David Ebershoff took over, Mitchell was presented with a substantial list of changes for the US edition, and “due to my inexperience at that stage in my three-book ‘career’, it hadn’t occurred to me that having two versions of the same novel appearing on either side of the Atlantic raises thorny questions over which is definitive, so I didn’t go to the trouble of making sure that the American changes were applied to the British version (which was entering production by that point probably) and vice versa”.

“It’s a lot of faff – you have to keep track of your changes and send them along to whichever side is currently behind – and as I have a low faff-tolerance threshold, I’m still not very conscientious about it, which is why my US and UK editors now have their assistants liaise closely,” Mitchell told Eve. “I really never dreamed back then that anyone would ever notice or care enough to email me about it, or that the book would still be in print 13 years later, let alone sell a couple of million copies and be studied or thought about by academics.”

Eve says that Cloud Atlas is not the only text to vary between its editions; he points to Andy Weir’s originally self-published bestseller The Martian as another novel with different editions, and has released for free the visualisation software that helped him compare the texts of Cloud Atlas, with the intention that other works of contemporary fiction will be examined by others.

“This is not a phenomenon unique to Cloud Atlas,” said Eve. “[But] given that this text is widely taught, studied, and read by many groups, there are some important questions to ask around how we are discussing novels and the specificity of the language within them … [It also] shows the dangers of prize panels reading from different editions and the importance of standardisation here. Cloud Atlas won many awards … But were all the members of the judging panels reading the same text? It’s an intriguing question that I haven’t yet probed.”

Both editions, Eve admits, were authorised by Mitchell, so in that sense both are definitive, but he believes the US edition is more widely distributed, particularly as it is the basis of the French translation and the film script. “Whether that mass dissemination counts as definitive, though, is something on which I cannot rule,” he added.

Mitchell told the Guardian that the fact an academic paper had been written about the two versions of Cloud Atlas would “teach me for not leaving ‘finished’ manuscripts well alone”.

“The UK version was submitted first and the US version some weeks or months later, so – if I was dead and couldn’t deny it – the inference would be that the American version is ‘more’ definitive,” said the novelist.

“Being alive, however, I’d ask readers to view the difference between the Cloud Atlases less like a director’s cut versus the original release and more like two very slightly different versions of the same song, recorded with the same musicians, in the same room, at the same session, with differences of only a few notes and a few words, which you can only spot if you concentrate intently. In this context, I don’t think what matters is ‘which is definitive?’ but ‘which works?’

“For me, in the case of Cloud Atlas, both work. Not that I have the faintest memory, after all these years, what the differences even are.”