Welcome, Chigo!
The fact that Anthony Coppola's name wasn't mentioned (but Nazorine's was) doesn't prove that he didn't attend Vito's funeral or wake. As you've no doubt noticed, there's plenty of sloppy writing in the novel. One such example at the funeral: "The Five Families sent their Dons and caporegimes, as did the Tessio and Clemenza Families [sic]." Tessio and Clemenza Families? It seems that Puzo suddenly made them "independent" at the Don's funeral--only to put them back under Michael's thumb the very next day.