Hi
This is my first post here. Thought I’d give the site a try. 
Hope this is the right sub-forum for this post.
I’m trying to get some varied opinions/views. What do other character artists do when it comes to adding a mouth bag to a character? Specifically, if you’re doing a high to low poly workflow? Do artists tend to make the mouth bag with the high poly, retopologise it, unwrap, and then bake to the low poly? Or do they/you add it afterwards once the baking has been done?
With a character project I’m currently working on, I did the mouth bag after baking, which caused problems as the new geometry caused my Normal map to break. I’ve since rebaked the low poly, but with the low poly including the mouth bag. However, apart from some minor issue with the AO bake of the lips, there’s a dent at the corner of the mouth. Once I’ve rigged and posed it with the mouth open a bit, that corner looks really messy. 
Here’s what it looks like in Max with the mouth slightly open; the bake in Substance Painter and then in Marmoset after the pose has been done:
I’m not really sure what to do in this situation; I’m out of ideas. And what would be best to do in the future.
Any help or suggestions would be greatly appreciated.