Despite Puzo's sloppy writing, I reiterate: it makes absolutely no sense for Vito and Mike to have waited 7 years to exact revenge. As I have posted previously, any number of variables could intervene in the interim: Vito's death; Mike's death or disability; Mike's betrayal or usurption by Corleone encumbents; Mike's imprisonment; the death of one or more of the five family dons; the death, disability, or imprisonment of Corleone encumbents; the enactment of laws.