Study based on almost 4 million papers shows that "in 8% of cases, authors managed to publish one manuscript three or more times"

 

https://www.sciencedirect.com/science/article/pii/S1751157721001176

See in the link above a recent study that found 70.000 duplicate papers. Still what is worse for science, paper duplication or the plague of fake authorship? https://pacheco-torgal.blogspot.com/2021/03/how-many-papers-can-superscientist.html