It looks a bit too neat for a cleft lip scar to me, but I’m no expert. Just basing it off repaired cleft lips that I’ve seen, the scar tissue is usually wider, and the lip usually looks “pulled” towards the nose a little at the base of the scar. And to graft skin over it I think would draw even more attention to the area - depending on where the skin was taken from, it more than likely would be a different colour, probably wouldn’t grow hair and definitely not in the same pattern as his facial hair if it did. It would be especially noticeable if it was something done later in life, when collagen production slows down and the body doesn’t heal as well as before. But he’s definitely had an injury to the area at some stage, and Tristan’s murderer was described as “EITHER having a cleft lip OR a large scar on his upper lip”. Also described as being 20-30 (CB was 22 at the time). I’d be very surprised if CB hasn’t been in a fight or two in his day.
It’s interesting you bring up skin grafts though, Owlpellet. I’ve always thought CB looks to have a graft at the top of his nose, between his eyes, in the attached photo. The skin is a different colour, it looks stretched and “shiny”. But it’s not evident in any other photo I’ve seen of him. Wonder could the scar the Irish barmaid saw at the top of her assailants leg/hip (I’m 100% convinced still that was CB) be from the result of having skin removed for grafting?