A bit limited, no? Obviously, no taxonomy of sex or gender will ever be completely satisfactory, but {unknown, male, female, not applicable} is missing some fairly obvious and useful additions, such as hermaphroditic and transgendered. I should have hoped that a standard taxonomy for gender would at least have a catch-all like "other;" "unknown" and "n/a" are not good catch-alls, as both make definite claims which may not be true for other genders.