NY Death Records on Vincenza, Carl and Eugene? (Eugenio?)

This needs more digging into ... Is the reason I cannot find the death record on Eugene Matisse (though he is in the 1920 Census) because he is listed as Eugenio???
What is the deal with people playing around with their names ...
FYI ... I work on a biometrics project and it will be great to have a unique, biological identifier that is robust, stable and reliable. Obviously, names don't cut it!!!