I have a Dopey (Dopey 2)who is constantly over groomed by Dopey 1. It generally takes a while to grow back, sometimes as long as a month after the initial problem was sorted (i.e. after we had to split them up because Dopey 1 was making it worse, once we separated them, it took about a month or so). We tend to separate ours temporarily because Dopey 2 ends up with huge sore bald patches (when originally it started with a tiny scratch, or on an injection site) and they are very easy to bond back together. We do supervised play, swapping cages, etc.
I found sudacreme moisturises the skin and speeds up the growing of the fuzz. Do you have that over there?