This one is one of those I-feel-dumb-right-now ones that creeps up on me each time I run into it: you've got a bunch of display or view modes available on a Drupal 7 site, and then a particular content type has a couple of those set as active at /admin/structure/types/manage/{content type}/display. Now: where on earth are those display modes actually used?
For my purposes, I'm lucky, in that most everything is nicely exported out to Features, so I can check the codebase to find display modes in use. What gets me is that display modes can be used in a couple ways. If the content type is being output by a view as a rendered entity, there's likely a view mode set in the view; that's the one I usually remember. But if the content type is being rendered directly as the output of a field using an entity reference, the display mode might be set on the display mode for that particular field from the referencing content. (Ohhhh, duh, yeaaaah....)
So when I'm looking for views output modes through the features code, it's helpful to search for ['view_mode'] = '{display_mode_name}' to find all views that use the display mode for any rendered entities; it might also work to look for '{content_type}' => '{content_type}' to find views that use specific content types, and then look up a bit in the feature code to see what display mode is used.
For entity references, though, looking for 'view_mode' => '{display_mode}' in the features code, which should get you into a block of field instance code, which hopefully offers some useful information tracking down the content type in use and the place the content type is used.
I suppose all of the above depends on healthy, clear use of machine names across views, content types, and field names, as well.
Once you use the above information to find a place to check rendered output (and, yes, I recognize I'm maybe doing a bit too much hand-waving here on that part) it's worth confirming the output is what you expect via checking the theme debug comments output via some relatively straight-forward theme debugging.