Yes, they publish the next year edition in August of every year. But they also do an incremental update early in the new year which addresses some of the things the writing team had to guess at back in August. The mid-year updated versions go to stores whose UG stocks are depleted, as well as all ebook versions. I couldn't find a written reference, but I recall the co-author, Len Testa, discussing the update schedules on the WDW Today podcasts. Len is active on the Touring Plans web site as well as these forums, if anyone wants to pester him directly. (He's responded to about 1/3 of my stupid questions.)
The Passporter team is much smaller and their annual release is a big deal. They also tend to blow out old editions at a steep discount in the weeks before a new edition is released. You can find out more details by checking out their website or following the "Passporter Moms Podcast".