Anim-Editor Body Parts limit?

Hello,
So I was just about to animate a rig of mine. This rig has like a ton of joints/body parts.
I started animating. However, I noticed that some of parts does not show up in the editor’s explorer. I’ve tried the plus (+) button/Add a new animation track and clicked on the referred parts, but they still don’t show up. The same result goes with Add All Body, too.

This makes it difficult for me, since I am unable inspect on one’s keyframes. Was thinking of this being a bug. But then I thought of this as some ‘limit’ feature. If that’s the case, why??

What should I do?