Nice exercices and shading! I noted the traps color extended to the Infraspinatus and part of the deltoid.
Otherwise they seem good.
Shading for the most part looks good, I mean, I guess if you want it to be even more accurate you could do a form base and see where shadows fall on things like the arm or how it wraps around the right left horn, but I think it still looks good with a bit of artistic liberty (I do it all the time).
What I mean is something like this: (I saw it in a Marc video, but not sure which one it was)
Do a 3D simple render of the geometric shapes that do your drawing. Something quick and simple.
This allows you to focus on shadows and lights and how these wrap around simple shapes, which are usually much easier to tackle than complex anatomy feaures. Add lightsource and basic shadows:
Put it over your drawing and you can use it as a guide to refine your shadows further adjusting as needed:
It's fairly quick to do. Some people will go a step further and buy a lamp to take a photo to use as a reference, or even model their shapes in a 3D tool to move the light around.
Honestly it's something I rarely do myself, but I'll probably try to do it more for some pieces. Pretty good to do for more elaborate ones.
Keep it up man, these are looking great!
