The last time this sort of thing came up in the romance field was when Janet Dailey plagiarized the work of Nora Roberts. In that case, Dailey eventually apologized, blaming it on "a psychological problem that I never even suspected I had ... I have already begun treatment for the disorder and have been assured that, with treatment, this behavior can be prevented in the future."
Plagiarism has happened in SF, fantasy, and horror as well. A few decades ago, Elsevier-Nelson was scammed by a plagiarist who copied out an entire Gardner Fox novel word for word and got it published by them under his own name. A university student submitted stories I'd originally published by Jeffrey Carver and Resa Nelson in Science Fiction Age as her own, and was found outthough as far as I know those were never submitted for publication, just to pass a class. Then there was the Craig Strete/Ron Montana contretemps, which seems to have been more an issue of an attempted collaboration gone bad than an actual plagiarism, and the time two sisters plagiarized Dean Koontz (though in that instance I'm leaving out their names because I don't believe that in the end that the sisters were found equally culpable).
I can't remember any other cases. And I can't recall any exactly like the Edwards situation, in which passages from earlier stories were incorporated without attribution in a new tale, and then professionally published. Any reason why we don't hear more of this? I'd like to think that it's because SF editors have been better gatekeepers over the years, and have spotted and winnowed out the plagiarisms before they ever got published. But surely it can't be as simple as that. Anyone have any other theories?
Meanwhile, remember the words of Paul Gauguin, who wrote, "Art is either plagiarism or revolution."