There was only one Godfather book. It covered all of GF I & II. The Sicilian only references the Corleones.
That’s always been a tight time problem, but the timeline of the studio head Woltz murder seems to be the morning after Hagen leaves the dinner. It was probably one of the other cuts that shows there was a week in between. Anyway, it’s real easy to see. They’re flying back and forth regularly anyway. And Tom has been out of the loop for a while. Michael, always way ahead of everybody else has already summoned Pentangeli’s brother , and he’s got him on ice. Works for me.
In the Epic, after Tom returns from Hollywood, there is a scene with Sonny and Vito where they discuss Woltz. Vito says Luca Brazi should go take care of things. Then they show the morning when Woltz finds Khartoum’s head under the sheets. It couldn’t possibly be the morning immediately after the dinner; it has to be at least another day or two. After that the scene shifts back to Tom, Sonny and Vito discussing the meeting with Solozzo. Next time I watch it I will have to look closely to see if they are wearing the same clothes, but I think they are.
At the time of Michael’s testimony to the Senate, they didn’t yet know that the feds had Pentangeli, or Michael probably would have taken the fifth. There would have been no reason to have Pentageli’s brother available until after they found this out. The scene with Pentangeli and the FBI guys is simply out of sequence. My guess is that it was done this way to imply that it was the 11th hour and Michael is SOL.