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.
Heh, some ISOs need to be updated. 1976 initially published and 2004 it was updated. Makes you wonder what other standards are out there, and are ridiculously out of date.