Yes, you two have both got it. The company was aware of the aliens' existence because of the events in AvP; it was even in Mother's log to tell Ash to bring back lifeform, and in Aliens, Ripley said that her crew went out to the planet on company orders to get this "thing". Maybe, like Heyroglyphsarenice said, Weyland-Yutani sent the crew to space on a regular mission, with Ash the android there just in case they encountered Alien life. Maybe the planet they drilled for oil was believed by the corporation to be the home of the alien species, and, when the company was disappointed to find this was not true, they sent them on their way back to Earth. However, they picked up the signal from the Derelict ship and traveled there, with Ash, Mother, and the company in high hopes for Xenomorphs. Well I suppose they got what they hoped for.......
~For centuries, human beings have worshipped these beasts as gods, beasts that will forever haunt us, beasts waging an eternal war.....~
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