After Fredo fails to protect his father from the assassination attempt, he is not seen again until the day Vito returns home from the hospital via ambulance?
Also...
Fabrizio, Calo and Michael are talking about New York/America and Michael only confirms that he is the son of a big shot. At this point, we assume Fabrizio and Calo do not know Michael's last name?
However, when Fabrizio is translating for Michael, he doesn't bat an eye when Michael tells him to tell Vitelli that he is Michael Corleone hiding in Sicily. Wouldn't everybody know exactly who him and his father were as soon as they heard the name? One would think so?
When Vito returned to Sicily and killed Don Ciccio, there was a large can of Genco Olive Oil on the table next to his dead body.
