Most Chinese surnames are ancient, but their romanizations are not:
* Names with the same pronunciation (homonyms) will probably end up with the same romanization. No romanization system has ever completely solved this problem, except by assigning arbitrary spelling differences.
* People will probably tell authorities the pronunciation of their name in their native language (Mandarin/northern dialects, Cantonese, Hakka etc.), which creates different-sounding versions of the same name. Worse, these romanizations are far from unified and don't correspond to the standardized romanization systems. Familiar example: Lee for the name 李 (Pinyin: Lǐ) and its homonyms.
* There are multiple romanization systems in use, which also yield different versions of a name, even if they all sound the same. A familiar example is Mao Zedong, whose name is Mao Tse-tung according to the Wade-Giles system, from before Pinyin romanizations of names became commonplace. For Cantonese names, a dizzying amount of romanization systems exist.
All of these render any surveys about Chinese names in the Diaspora extremely difficult, and most statistics completely garbage. For some families it might be impossible to recover the actual surname.