How to adapt the date format in the admin/content page? Each Article shows "Authored on YYYY-MM-DD" date per configured regional date format. e.g. 2015-05-14 00:00:00 +0100

However, the content listing at admin/content shows the UPDATED date as MM-DD-YYYY unlike anything else and is confusing to admins.

Users have no choice of Default Time / Region on the Drupal 7.37 site. 
Date and Time Long, Medium, Short formats are all ... YYYY-MM-DD
Date (and time) formats can be configured via admin/config/regional/date-time. It can be used to specify the format for data types Long, Medium and Short.

Other tabs that are available on that same page:


Formats (to define your own custom formats).
Localize (for language specific tuning).
Date Views (for date views specific to "day", "week" or "month").