My mom is going to chess classes for some years now. Am absolutely noob. She has been asked to buy a book: "Modern Chess Openings" by Walter Korn. While googling, I came to know that the author of this title is changed over edition. Till MCO12, it seems that it was completely written by Walter:
Now MCO14, 15 completely erases Walter's name from the book:
Is the content of the book considerably changed over these editions. Which one should I prefer?