In The Voyage Home, the scriptwriters took great pains to point out that Scotty and McCoy were not changing history by giving Transparent Aluminum to Dr. Nichols, since he "invented" it anyway. Makes me wonder how and why they were so careless for the rest of the movie. The Bird of Prey was at least partially decloaked in front of a couple of trash collectors, plus a whaling ship (granted they may not have been believed if they'd spoken up in public.) But then: during the rescue scene in the hospital, Kirk openly fired a phaser to melt a lock in front of an entire 20th Century medical team -- and McCoy proceeded to cure Chekov's head trauma in front of the same team (those folks were watching *very* closely) using the whistly forehead device. In escaping the same hospital, the entire group ended up disappearing from a supposedly closed elevator. After all that hilarity ensued, I'm sure somebody also put two-and-two together about the dialysis woman and her miracle kidney. Not to mention Chekov leaving a couple of pieces of future technology in the hands of the United States Navy. Granted it wasn't functional at the time, but after all the other magic that happened around Chekov in the hospital you'd think they would pay a little closer attention to those pieces. Finally: I've always wondered whatever came of Bob, Dr. Taylor's colleague at the Cetacean Institute. From his perspective, Taylor slapped him, ran away from him in a rage -- and then completely dropped off the grid. Never even went back home to wherever she lived, never came back to work... the most they could have discovered was that her pickup truck was abandoned in Golden Gate. Poor Bob!