Generalizations of the type you seem to be trying to make aren't valid, end of.Some humans are born without limbs, too many limbs, additional fingers, or even without a cerebrum, or with disabilities. Would you say that therefore: Humans have more than 2 legs and 2 arms, humans have more than 10 fingers, or that humans do not have a cerebrum, and humans do not walk or cannot see?
And what is the connection to the original statement of "more than two sexes"?
Because we are all of the same species, there are genetic and developmental commonalities between most of us, but there is variability, and statements of the type "all people are either ___ or ___" that are under discussion don't hold absolutely. Such statements are exclusive and false: they deny personhood to people who don't fit into those categories, and their falsehood follows from the self-evident self-contradiction of denying personhood to a person. The truth in these cases would be closer to "most people are either ___ or ___, but some aren't."
Most humans have two arms and two legs, but some don't. Some people have more than ten fingers, some have fewer, but most have exactly ten including the two thumbs. And so forth.