Its a Drupal 7 site so every content item has a publication date in the db since it is part of the root data schema for posts/pages and all sub-types. In their case they have at least two content types in their news page. All of the "News" type articles do display the date but the template for "Research" articles does not display it. It is possible this was deliberate but most likely it just was in the default news template and when they created a custom template for the research articles they based it on the default page template which doesn't include a date line.