Simplify the following text for a Grade 9 native English-speaking person.
Original: Actually , you can say that the 10th edition was only an extension to the 9th edition , and the 12th and 13th editions were extensions to the 11th edition .
Simplified: The 10th edition was only a supplement to the 9th , just as the 12th and 13th editions were supplements to the 11th .