Extensive plagiarism

An article published in Journal A in 2003 contains extensive, almost verbatim, unattributed quotations from an article published in Journal B in 2001. The editor asked a member of the editorial team to compare the two articles line by line, and there appears to be a high degree of overlap without any reference to the original article in Journal B. The authors of the article and the editor of Journal A were asked for an explanation. It’s hard to see that there is any explanation apart from plagiarism. The authors of paper A claim that there is only 5% overlap between the two articles.