The edition I used in scheduling the reading was copyrighted 2005, but I also included the chapter titles in addition to page numbers so that people with different editions could use the chapter title to find the right page numbers. I don't think it would be hard at all to swap out editions. One person even told me she was using the smaller Science Explorer books from the series, rather than the Physical Science textbook, and that was working out for her too. (She did mention that the books include a small number of chapters that were not included in the compilation.)