Factual error: Master Sergeant Alexander "Al" Apone U.S.M.C. ranking was wrong on his uniform. His uniform showed a U.S. Army Sergeant First Class rank. (You can see this when they were loading up on their APC.) The correct ranking should have been 3 chevrons up, crossed rifles in the middle, and 3 rockers on the bottom. *Yes, in the future, the ranking system could have changed.*
Factual error: The marines' rifles are supposed to fire "standard armor-piercing rounds", which should have done way more damage than producing a few sparks on the frail sheet metal table in the med bay when Hudson shot the face-hugger threatening Newt. "Standard AP rounds" would have pulverized the table and created a huge hole in the wall behind it.
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.