I'm glad to hear that he's making progress, even if slight.
The litter habits will likely get messy for a couple of weeks with a new bunny because they will both wanting to be marking their territories. It should settle down again, though maybe not back to the 99% you're currently getting
For those of you who've brought back a new bunny to meet your old one(s), did the territory incursion ever affect the old one(s) litter habits? Did you have to retrain them or did it just get back to normal on its own?
The litter habits will likely get messy for a couple of weeks with a new bunny because they will both wanting to be marking their territories. It should settle down again, though maybe not back to the 99% you're currently getting