When Marty is about to travel back to 1985 in BTTF 1, he emphasizes that Doc read his letter (about Doc getting shot by Libyan Terrorists during Delorean Test, 1985). However, in BTTF 3, when Marty is back at Doc’s mansion, after Doc just saw Marty one head back to 1985 (from first movie), Marty doesn't try to warn Doc about getting shot. Now you may say he just assumed Doc read his first message, but couldn't he have also thought it possible that Doc only read it because Marty 2 told Doc about it? Also, in BTTF 3, after Marty gets hung by Mad Dog Tannon, Doc asks Marty,
"Marty, what idiot dressed you in those clothes...".
Shouldn't he know that he dressed Marty that way in 1958.