I am not sure about how they came up with the folks mentioned. Beckham does not seem to fit the bill, I may be missing something. I am a big fan of Past Lives and New Age beliefs.
There is one Native Tribe that talks about 3 sexes
This is from Wiki
https://en.wikipedia.org/wiki/Third_gender
Third gender, or third sex, is a concept in which individuals are categorized, either by themselves or by society, as neither man nor woman. It is also a social category present in societies that recognize three or more genders. The term third is usually understood to mean "other"; some anthropologists and sociologists have described fourth,[1] fifth,[2] and "some"[3] genders.
The state of personally identifying as, or being identified by society as, a man, a woman, or other, is usually also defined by the individual's gender identity and gender role in the particular culture in which they live. Not all cultures have strictly defined gender roles.[4][5][6]
In different cultures, a third or fourth gender may represent very different things. To Native Hawaiians and Tahitians, Māhū is an intermediate state between man and woman, or a "person of indeterminate gender".[7] Some traditional Diné Native Americans of the Southwestern US acknowledge a spectrum of four genders: feminine woman, masculine woman, feminine man, and masculine man.[8] The term "third gender" has also been used to describe the hijras of India[9] who have gained legal identity, fa'afafine of Polynesia, and sworn virgins.[10]
While found in a number of non-Western cultures, concepts of "third", "fourth", and "some" gender roles are still somewhat new to mainstream western culture and conceptual thought.[11] The concept is most likely to be embraced in the modern LGBT or queer subcultures. While mainstream western scholars—notably anthropologists who have tried to write about the South Asian hijras or the Native American "gender variant" and two-spirit people—have often sought to understand the term "third gender" solely in the language of the modern LGBT community, other scholars—especially Indigenous scholars—stress that mainstream scholars' lack of cultural understanding and context has led to widespread misrepresentation of third gender people, as well as misrepresentations of the cultures in question, including whether or not this concept actually applies to these cultures at all.[12][13][14][15]