Did David and Weyland know about LV-426 existence?

If the Bluray extra's are considered canon, then yes, they did know. We'll have to see if this is elaborated on, in the sequels.

This topic has been mentioned quite a few times, even recently; [url=http://www.prometheus2-movie.com/community/forums/topic/12212]David knows about LV426[/url] [url=http://www.prometheus2-movie.com/replies.php?id=10779]LV-426 Explained: Weyland knows about it but deters others from knowing[/url] We urge everyone to use the "Search" function provided to be sure something has not been discussed before. We do not frown upon resurrecting older threads, and commenting on them, in fact we encourage it. When searching a topic, use Google ( Example: Engineer Speaks, Prometheus2-movie.com ) for post bodies and the "search" function for post titles. *locked/duplicate thread