You are right about what happening to Clemenza and Pentangeli on-screen in GFII. There's no reference to Clemenza as a traitor, and Frankie was his successor.
However, the posters above are referring to FFC's original plan for Clemenza in GFII. Richard Castellano (the actor who portrayed Clemenza) and FFC could not come to terms for him to appear in the sequel. So Clemenza was killed off and the character of Pentangeli created to replace him.
What SC is saying is that the plot line originally mapped out for Clemenza was substantially the same as that eventually developed for Pentangeli.
Oh OK, now I understand. That is great information on what might have been. I'm glad though it didn't work out that way. I would have been disappointed if Clemenza would have turned. Since Pentagali was a new charactor, I was not let down by him "flipping". I did like though that he did the right thing in the end.
