The LOs might be spliced, we don't know what Ink was doing in the devil's workshop. But as far as the regulars are concerned, it should be some outside 'natural' phenomena that turned them. It was 3 or 4 months after the initial outbreak before we saw the LOs. Tanya might not be able to find how/why the LOs differ but she may find how/why the regulars are. We have not yet been inside the brain of a zombie. But will Tanya's skills reach that far?