Continuity mistake: When baby Clark lifts up the truck, Martha's grip on his husband changes: In the close-up she grabs his chest, but in the wide angle she grabs his ribcage. This changes back and forth several times.
Continuity mistake: While Lex and Otis are talking with the lieutenant and his crew at the bridge, the sun changes between shots.
Continuity mistake: In the extended version, where Martha is preparing breakfast, she places a box of Cheerios on the table. Then she looks out the window at Clark. The shot changes to an exterior shot of her looking out the window, but there is a pitcher of milk next to the box of Cheerios that was not there before.
Continuity mistake: While Lex is telling Superman his plans with the missiles at his home, he is touching his cane with both hands then only then both hands back again.
Revealing mistake: When the helicopter gets jammed on the white railing at the ceiling, Lois is replaced by an obvious dummy that dangles back and forth with no control.
Continuity mistake: While Lois and Superman are being mugged in the alley, Lois kicks the thief and protects herself leaning with her face against the wall and her arms widely spread. A frame later, when Clark grabs the bullet, her arms are close to her head.
Revealing mistake: As Air Force One enters the frame from the right, there appears to be a set of tracks faintly visible under it.
Revealing mistake: When the helicopter is hanging off the roof, a safety securing cable is attached to the fuselage to keep it in place.
Continuity mistake: In the extended version, in the scene where Martha is preparing breakfast, in the interior shot, she places a box of Cheerios on the table. Then she looks out the window at Clark. The shot changes to an exterior shot of her looking out the window, but the angle of the box of Cheerios has changed. (00:38:35)
Continuity mistake: In the extended edition, before Superman enters Lex's lair his hair is short, then when he's being shot at, his hair is much longer and bulkier. When he finally enters the place, it's back to short.
Continuity mistake: The two cops are following Otis at Grand Central Station and two girls, one in yellow, pass by their left side. When the angle changes to a closer one, the girls are in the back and pass by again.
Continuity mistake: Lois exits Perry's office and Clark enters to talk about salary. His hat swaps from facing up to down between shots.
Continuity mistake: When Clark is about to jump in front of the train, there's a crossing sign shaped as an X. Depending on the shot the front upper left part is either bent and about to break, straight, or missing.
Continuity mistake: When the Kent's stop the truck and see the cradle, the sky swaps from sunny and clear to heavily cloudy in a second.
Continuity mistake: When Kent's father pulls over his car, he holds the steering wheel with his right hand on the top. From the side, barely a frame before, he has his left hand on the side.
Continuity mistake: The way the bags are positioned in the Kent's pickup differs between the side and back angles.
Continuity mistake: In Lex Luthor's lair, the bottles to the left of the TV broadcasting the news disappear in the following shot.
Continuity mistake: When hanging from the bridge, the damage on the school bus' hood is different depending on the shot.
Continuity mistake: When Ms. Teschmaker is sunbathing, the trolley by her side is close to her thigh. In the wider angle is by her ankle.
Continuity mistake: When Jimmy runs towards Hoover Dam his hair is long. A fraction of a second later it's very short.
Answer: There are generally two methods of time travel. Skip vs Slide. When you slide through time, you are in essence rewinding or fast forwarding a tape. Time will accelerate to the desired moment. This method, the traveler will witness the rewind and will only allow one of them to exist. When skipping, you are plucking yourself from the time stream and placing yourself in the desired moment. This method, travel is instantaneous and can allow for multiples of the traveler to exist at once. Superman rewound time. He used the slide method and went directly to Lois after doing so. This means those he previously saved...died after his reversal.
Or he could have used the skip method. Like you said, it enables a traveler to pluck themself from the time stream and placing them at the desired moment allowing for two Supermen to be able to prevent both missiles from reaching their destinations.
He couldn't have used the skip method if he rewound time.
Bishop73