Trails and parks change at an alarming rate. First editions take a long time to write so that by the time it is almost ready to publish, some of the places many have changes. Subsequent editions need a revisit of every park or hike before publication. The author(s) may do much of this as they should be familiar with what might have changed or gotten notices about changes. It is useful to have a second set of eyes as others see things that an author might miss.
Know the New Hiking How-tos