Just how similar passages showed up in two books is a tale of how the largely obscure $4 billion a year world of elementary and high school textbook publishing often works, for these passages were not written by the named authors but by one or more uncredited writers. And while it is rare that the same language is used in different books, it is common for noted scholars to give their names to elementary and high school texts, lending prestige and marketing power, while lesser known writers have a hand in the books and their frequent revisions.
As editions pass, the names on the spine of a book may have only a distant or dated relation to the words between the covers, diluted with each successive edition, people in the industry, and even authors, say.
In the case of the two history texts, the authors appeared mortified by the similarities and said they had had nothing to do with the changes.