Some chapters and paragraphs of the Japanese paperback edition were not included in the English translation. Combining the original three-volumes (Japanese) would have been too long, and so the publisher requested that ~25,000 words be cut for the English translation.
For example, the two missing chapters from the second volume of the original three-volume elaborate on the relationship between Toru Okada and Creta Kano, and a "hearing" of the wind-up bird as Toru burns a box of Kumiko's belongings. In the third volume, the computer conversation between Toru and Noboru Wataya and Toru's encounter with Ushikawa at the train station are also omitted.
In addition to reducing the word count, some chapters were moved ahead of others, taking them out of the context of the original order.