Also, another problem with duplicating field values into Post Type A from Post Type B: those fields in Post Type A won’t reflect any changes made to that field in Post Type B. (E.g. I can load ‘last_name’ from Post Type B when creating or updating Post Type A; but it won’t dynamically update if Post Type B ever updates that field.) That’s why the posts_join seems like it might be the solution without slowing down the site too much.
