Let me answer your question with a question: why did Sergey (or Sergei, as some would say) Bubka's passport have Serguey on it? Because whoever transliterated from the Cyrillic didn't understand the conventions well enough.
Similarly, it has generally been the policy of statisticians to ignore transliterations (even from athletes themselves) if they appear to be "wrong." Having said that, I have no idea how to transliterate to get Kenteris or Kederis. Or why ATFS has athe Greek high jumper as Bakoyianni when she had her own website saying Bakogianni. (I've purposely ignored the diacriticals here.)