Well TB, as you state, I do think that sloppy writing plus authorial license explains alot about what you cite. Also, cramming weeks if not months and years into a 4 hour film is also a factor. Fredo was desperate, it seemed, for recognition. Such desperation combined with his inability to decipher scheming by and motives of others made him vulnerable to flattery and blandishments. So, I don't think Fredo was capable of looking ahead.

On the other hand, Frankie's meeting with the Rosatos was only set after Michael visited Frankie at his home and not right after the shooting, right? Fredo found out about the meeting because Ola told Fredo during the late night telephone call.