A friend of mine just read the book for the first time, and she brought up a point I'd never even thought of.
Unless Lucy was pregnant before she went to Vegas, how is Vincent Sonny's son?
I could be missing something really obvious here, but I just can't work it out.

Hi Liz_85 i have thought about this as well, because in the book it doesn't say anything about Lucy being pregnant or having a kid and she did sleep with jules so maybe it is hers and she could be trying to get money out of the Family.

It's an interesting debate but generally the book and movie are regarded as being seperate. Vincent was made up entirely for Godfather III, it's a slight plot hole and I guess we're just supposed to believe it.

Another example of the book v's movie being different is the fact that Michael has 2 sons in the novel and a son and a daughter in the film.

Another difference is that: in the book; Fredo is supposed to be big and strong. Not as wimpy as he was portrayed in the movie. Also; Sonny is supposed to have: curly black hair. Carlo supposed to be slightly build, and blondish.

At Connie's wedding, Puzo describes Carlo as having "worked in the desert air while very young--heavy laborer'work. Now he had tremendous forearms and his shoulders bulged the jacket of his tux."
Re. Vincent as Lucy and Jules' son: I think Lucy's gynecological problem may have prevented pregnancy.

I to believe that it is a plot hole we are just supossed to believe.

the movies trilogy is not supposes to follow the novel. puzo and coppola confirmed this when they started making part II.

Really, I thought Fredo was portrayed just like he is in the movie. **SPOILER** (such as when Brando gets shot and he fumbles around with his gun and starts crying) **END SPOILER**