Can't he only reassemble things he destroyed himself?
It was stated he had cured people with chronical illness so I think it's pretty much safe to assume that he can reassemble any material.
Also I think your statement is kinda correct. I mean a bulletwound in his arm. If he intends to fix it, I'd assume he'd have to disassemble some flesh and tissue around the hole and then reassebmle the are the way he wants. On the other hand, can he create "the extra tissue" that is missing from the bullet hole?