How to process the result of a view?
Views can be great for some things, but sometimes it can add more complication then it is worth. Trying to achieve this in views seems like it could be one of those situations. 

If you are familiar with coding, it might be easier to process the list of authors, grab the entity_reference from them, create an array from those where you don't repeat the values and then output the numbers associated with each value.

If looking to do this solely in views, you could use https://api.drupal.org/api/views/views.api.php/function/hook_views_pre_render/7 to grab the results and process them and then output the rows as desired.