Well, today was the day the vet said I could take the bandage off....
...so I did.
Here's how it looked after a good clean and pulling away all the fur and dead skin that had grown into the hole:
The proud flesh is probably about the width of my thumb, but not as thick. It's spongy, but not sensitive.
I sprayed it with silver spray as instructed and... just left it...
Mattie didn't seem particularly relieved, but I am!
If it heals over there will be a mahoosive scar, but I don't think it should cause him a problem.
I hope his swollen fetlock starts to go down a bit now.
The original injury was 30 August, so just a shade under 3 months. I've just scrolled back through this thread and I can hardly believe how much it has shrunk and how well it has healed. Fingers crossed it goes on healing!