He didn’t. He was a non-English speaking nine-year-old who was surrounded by adults during the depression. Children are told correcting adults is wrong, it certainly won’t happen in another country.

It was the man who approved his entrance, not paying attention, who mistakenly took the city he was from as Vito’s surname. The important question isn’t why did he keep the incorrect name, but why on earth would he fight the system, as a foreigner, to get back his surname? There is no reason.