Older, evergreen content has always been a nice traffic source for digital publishers. But two years after The New York Times identified archival content as an untapped source of traffic, several publishers have grown it into something substantial, with some now generating nearly 40 percent of their monthly traffic from old pieces. They’re doing it by updating their stories more frequently, often multiple times per year, creating new sections and contexts for their content, and disseminating it at strategic times via social media and newsletters.