Continuity mistake: When Ripley enters the hive, right before she lights the second flare, she fires a flamethrower burst. When she does, the starter flame goes out, then in the next scene it is on again. (01:53:50)
Continuity mistake: From Director's Cut. The scene where Al is being quizzed about the ownership of the discovery of the object discovered by the "Mom and Pop" survey team tells us that a call has been put in by that team to the base. But then when they discover the ship, where is the call? They explicitly do not call it in. Now this is not just a general enquiry because they were sent out there two weeks ago to a specific grid reference. "He says he's onto something." (00:16:34 - 00:18:38)
Continuity mistake: When Ripley loads the magazine into the gun as she prepares to rescue Newt it says 95 rounds but when she is going down the elevator shaft it says 42 without her firing a shot.
Continuity mistake: Hicks gives Ripley a wristwatch which is linked to his tracker. If you look at the watch, its face is mostly black with a tiny portion that is clear. However, when Newt has the watch and falls down the tunnel and is wandering around the pool of water before Hicks and Ripley find her, you can see that the watch face has no black - it has a full clear face and appears to be a standard digital watch of the 1980's era.
Continuity mistake: When the crew is having breakfast the first time, at the end of the table is a non-moving kinetic orbit toy in 2 shots, then in the 3rd shot it's moving with no one touching it.
Continuity mistake: When Ripley is driving the APC, the passenger side front tire is on fire and engulfed in flames. When she runs over the alien with the same tire, the flames are completely gone. In the next shot and several shots after, the tire is completely engulfed in flames again.
Continuity mistake: In the beginning, Ripley wakes up in a sweat, practically crying. She rings Burke on the visual phone and she has a droplet of sweat on her nostril, but it's there, then it isn't, then it, is; it comes and goes.
Continuity mistake: When Ripley pulls Newt out of the cocoon, she has cocoon stuff all over her back, but a second later it's gone.
Continuity mistake: When the team approaches the colony entrance to open the outer door, all the marines are inundated with pouring rain. Yet the moment they enter the compound and start searching, they are all dry.
Continuity mistake: In the beginning, when they find the colonists, they have IDs under their skins, but on the read-out there's only about 6 of them, when there should be about 100 of them. Later, on the read-out, we see the right amount of IDs.
Continuity mistake: As the ship carrying the marines to the planet where communication has been down for too long, the pilot of the ship says, "Where's the damn beacon? Oh, I see it." But when she says the last bit, there is no vision of the beacon; it only comes into sight a few seconds later.
Answer: The company doesn't wait 57 years, they built a colony on the planet over 20 years prior to finding Ripley. The company was apparently unaware of the exact location of the derelict spacecraft. After finding Ripley and obtaining information from her, Burke was able to send the Jorden family to the precise location of the derelict spacecraft.