Sometimes when a glider has a large wound, the wound will close up, but the fur will not grow back. Or there might be a scar. Or both. Sometimes the fur will grow back all white or all black.
This is normal and does not impact the glider's ability to move or live a normal life.
Here are photos of a glider with a large wound that took a very long time to heal. He now has a large scarred area with patchy white fur growth.