New claim to authorship of published paper

In October 2011, our journal received a submission from author A with co-authors B, C and D. After review and revision it was published in mid-2012. In April 2013 we received a complaint from author X, saying that the work published in this paper was his work, and that although author A had been his research supervisor at the time the work was done, authors B, C and D had either little or no input to the work. Author X said that the correct authorship should be X and A in that order.

Author X provided as evidence an internal document submitted to and accepted by the university authorities in May 2010 in fulfilment of a requirement to demonstrate capability for research. His academic record confirms that this submission was successful. He then changed supervisor (and department) within the same university due to a breakdown of relations with his previous supervisor, and proceeded to complete his PhD in January 2013.
The internal document is not in English, but it is apparent that close to 75% of the content of the journal paper has effectively been taken from the internal document. [This has been checked roughly through the use of online translation. The majority of figures and diagrams are clearly the same. The authors (A–D) of the published journal paper do not appear to be contesting that this document was the source of the text although they claim ownership of the data and ideas.]

When challenged, author A says that author X was a poor researcher and was away from the country for considerable periods of time when he should have been doing the work. He also suggests that others in his research team gave author X considerable help with the internal document. He claims that author X has fraudulently used the work of author A and his co-workers, both in the internal document and in his PhD thesis.

The editor’s suggestion was that author X’s name should be added to the authors of the published paper, as second author (compromising on the initial request of author X that he should be first author, given that author A was the team leader, had a strong interest in the work and that this complaint had come nearly 3 years after author X had departed the group, amid some acrimony). This would be achieved through the publication of a corrigendum. Author

A disagreed strongly, and said that he did not wish his name to be on the same paper as author X’s. Author A also encouraged the other co-authors to respond, and they supported him. The original authors said they would rather withdraw the paper than have author X’s name added.

The editor indicated that withdrawal (retraction) of the paper was not an option at this stage, as no one had questioned the science in the paper, and the concern was solely over the authorship. The editor also pointed out that the guidelines on authorship, available through the journal’s web page, made clear that anyone who has made a significant contribution to the article should be included in the list of authors. The prior existence and acceptance by the university of the internal document as proof of the research competence of author X would appear to be sufficient proof of a significant contribution. This would not apply if there had been some formal challenge within the university, but no challenge appears to have been made.

The current head of department of author A has largely confirmed the picture painted. He says that when author X first came to the department he was announced by author A to be a ‘brilliant student’, but that relations started to break down early on, as author X had expected to do research in a somewhat different area. He confirms that after the internal document had been submitted and accepted, author X moved to complete his PhD in a different department, although in the same general area as before. He agrees with the proposed action and says he will attempt to convince author A, but with no feedback as yet.

Questions
(1) Can the journal make a decision to add author X’s name without the agreement of the other authors? Given the opinions that authors A, etc, have so forcefully stated, this seems inappropriate.
(2) Could a corrigendum be used to demonstrate the full order of suggestions—that author X be added, that authors A, B, C and D said that if that were decided they would withdraw their names, and therefore the paper would now be acknowledged as the work of author X alone?
(3) Should the request of author A and others that the paper be retracted be accepted? This appears entirely inappropriate as no one is objecting to the science or claiming that the work should not be published on scientific grounds?