Consider the t0 the moment of site starting and t1 the moment you add SSL to your site. All the FB, Twitter, etc. shares are stored according to the complete URL string. All the posts between the t0 and t1 will have the URL without 'S' and all the posts between t1 and 'now' will have the URL with 'S'. You can collect the shares from the FB API but you must provide the post URL and then concatenate the results. With this method you can preserve the shares, but we must keep this in mind: a share is registered with a single URL string, and also we must consider this transition as a one way transition and don't change it back to HTTP.