I am under the impression that Nemesis was originally a standard Mr. X Tyrant model who was injected with the Nemesis Parasite. If you look at his skull and look at the matter, biologically, you could say his nose, ears and, I imagine, his right eye, were eaten by the Nemesis Parasite and they had to stitch him up afterwards as a result. I reckon this has something to do with what Wesker's Report stating how a host would be eaten alive by the Nemesis parasite within five minutes if the Ne-T virus was not administered to the subject beforehand.
Perhaps the Nemesis Parasite partially consumes the flesh on the head before the Ne-T virus makes it adapt to the body?
