here blueemu it say on the front these exact words: McKay Chess Library, Modern Chess Openings 15 Edition
NIck de Firmian
3-Time us chess champion
Completely Revised and updated
Yes, they ALL say that - nobody is going to buy a new book advertised as "with 10% new content!"
But if you take yours and find someone with the previous edition to compare, you will find 90% was simply carried over. The new material will be in the most common lines like the Sicilian and Ruy Lopez, and the lines which were always changing like the Meran or Winawer Poisoned Pawn or Nadjorf Poisoned Pawn, etc.
Be sure to check out the footnotes, too! You will be shocked at how many have simply been copied from the last one, only the numbering changes.
Is this supposed to be shocking? It only makes sense to only update the openings that are changing. Some parts of opening theory change all the time and others only occasionally. I agree it's probably not a good investment to purchase the new edition every single time it comes out but anyone who has ever had to buy college textbooks can tell you that.
yes they put the updates on them.