I posted this question:
While I think it's a valid question, it is kind of a duplicate. I just realized that this behavior is happening because my vertex groups were locked on my mesh, which kept them from being updated.
As such, the question I link to in the post solves my problem. However, I still think it might be valuable knowledge to provide this information regarding unlocked vertex groups, especially since I think that the nature/function of Blender may draw its fair share of newbies like myself.