Time line of Prometheus and Alien movies

As you watch the inquest of Ellen Ripley on Aliens it helps to look at the timeline that prometheus, alien and aliens took place. The following dates are approximate and there is a point I want to make afterwards Prometheus: 2093 Alien: 2122 approx Aliens: 2179 which is 57n years after the events on the Nostromo took place. What is puzzeling is why the inquest commitee members clearly do not have information regarding xenomorphic life forms. One of them states that in 300 explored worlds never once did they encounter a creature like Ripley discribed. I can only imagine the the Weyland-Yutani corp. at this point in time, has compartmentalized the information regarding xenomorphs for only specific persons such as Ash due to the evidence of directive 925 in Alien where Mother, the Weyland programmed computer on the Nostromo states that the ship was rerouted to the co-ordinates to investigated and return the lifeform, which all other priorities recended and crew expendable. So Weyland corp. clearly knew about the existance of xenomorphic life forms and wanted them 57 years before the inquest. Even Carter Burke, clearly didnt initially know at the time of the inquest but his profit driven interest was peaked afterwards, which is why he sent out the wildcat mom and pop team to investigate the grid co-ordinates beyond the alien ranges on LV 426 without warning. He later explains that the reason he did not warn them was he did not want to create a security situation which would make it impossible for anyone to take advantage of the xenomorphic lifeforms Ripley discribed in the inquest. He wanted to capture the lifeform and get it back to Weyland's bioweapons division as he stated. This is my explanation as to why the inquest commitee appears not to be aware of the existance of xenomorphic lifeforms and does not believe Warrent Officer Ellen Ripley at her inquest.