At the moment, a question can have multiple duplicates linking back to it, but once you link backwards from a duplicate there's no way to link forward to later versions of the question....which makes it hard to find other possible answers.
I think it would be beneficial to have a list of all duplicates listed in a Duplicate Questions sidebar similar to the current Linked and Related sidebars. (Questions that are both linked and duplicates, as often happens, could be just listed as Duplicate.)
The Duplicate Questions sidebar could appear on the page with the original question, so that it links forward to any duplicate questions that have been answered. (Or it could appear on all pages that are duplicates of another, but this probably isn't necessary because the questions closed as duplicate already link backwards, even though they don't link to other duplicate versions.)
This feature would be particularly useful for questions that have been asked many times (and thus have a dozen different duplicates scattered throughout the site).