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The pages were published in July, but today have a pagerank of zero (the only ones on our site that are zero). Ranking and visitors have declined since the first few weeks after publication.
I guess it is possible the PR hasn't been updated yet, but we think it is more probably a penalty due to duplication because, despite having a completely different emphasis, many sections of text are identical to the original articles.
For future articles I guess the lesson is not to adapt, and to instruct authors not to re-use any text.
In the short term, however, we have to decide what to do with these pages. Our options are, I think, to leave, delete or re-write them (using same or different page URLs).
I would like (with the original author's involvement/permission) to rewrite them, using the same page URLs. However, I'd appreciate whether the experience in this group is able to foresee any problems with this that we haven't anticipated.
Your suggestion that future articles need to be originals without repeated text is very valid - although there may be good reasons for certain pieces of text to be repeated on various sites, Google seems to have overlooked this, and has grouped it all together as "bad."