Modern day Tenzing's last name is Norgay but in this article it's Norkay. I wonder when the change occurred and why...

Edit: part of the article hints at the answer, "when Tenzing Norkay, or Tenzing Norkay Sherpa, came to Darjeeling in 1933, he was treading a well-worn path. This is the way he has decided to spell his name—he now has business cards—but a European anthropologist who knows Tibetan says that “Tenzin Norgya” would be a better phonetic rendering, and that an accurate transliteration would be “bsTan-aDzin Nor-rGyas,” the capital letters representing the stresses."