It looks like Will is making excellent progress.
I've had a taste of this condition before (stroke). It feels as though the electrical connections to the muscles are disconnected or a very poor connection. It affects the smaller muscles the most (like the finger muscles). I remember having to cut the fingers out of rubber gloves to put them on (don't remember why I needed those gloves). The fingers were just too floppy - no way they would go in the holes. Every morning, I'd check to see if I could straighten my fingers and make a flat hand. For quite some time, a main challenge was to put paper money into a wallet - I'd just give up and mash it in there. Legs and feet feel like clubs when first able to walk again.
The way the medical people explained it ---> when the nerve cells die in the injury, adjacent cells take up the slack and become nerve cells (as long as there is some connectivity). But this takeover period can take literally years. Even after a couple of years, there may be things that are difficult, then after four years you can do it without even thinking. Depends upon the extent of the injury, I guess.
Although I'm certainly no expert on this stuff, Will has movement everywhere, so I think this a great sign for a nice recovery. It'll just take time ....