I think everyone has lagging body parts, even pros. But in my opinion, a lot of it is genetics. Take a big, noticable body part like quads. Some bros can build huge quads and some can't. You will see this clearly in every state level show you go to. BB'rs with better genetics tend to be more complete & symetrical, able to develop full, rounded, defined muscle bellies.
So how do you attack lagging body parts? A lot of the articles in the muscle mags have pros saying they do an extra this or that to further stimulate them. I'm skeptical on that one. If the extra volume could stimulate quick growth, wouldn't you be doing that same volume on all body parts?? Maybe if you underworked strong bodyparts and properly worked lagging parts you could catch up, but, who does that?? No one. So, I think its a slow process of fully recognizing what your weak parts are and making damn sure your optimizing your training to make sure they have every opportunity to catch up. And over-time they should even out more (although probably not completely, "perfect symetry" is extremely rare, not achievable for most and largely subjective anyway).