Module not reporting Drupal core version

I noticed that some sites are not reporting the drupal core version..

The logic is the following:

      $system_modules = system_list('module_enabled');
      if (strtolower($module_info->info['package']) == "core") {
        
        // if this is part of a project, only set the project.
        if(isset($module_info->info['project'])) {
          $res['core'][$module_info->info['project']] = array("version" => $module_info->info['version']);
        } else {
          $res['core'][$module] = array("version" => $module_info->info['version']);
        }
       }