Continuity mistake: During the bridge collapse scene, when Olivia is crawling on the beam, she is first seen on the part of the beam that is closer to Sam. Almost instantly afterwards, she is on the part of the them that is closer to Molly. The space between the two beams increases significantly between the two shots as well.
Continuity mistake: In the premonition right near the end, you see the truck hanging over the bridge and that is how the poles and that sheet of metal kill two of the main characters. Yet when they run to the end of the bridge, the truck is not hanging over the edge.
Continuity mistake: When the bus is falling into the river, some items fall down on to the window with Issac. However the camera cuts and the items have disappeared. (00:13:40)
Continuity mistake: When Peter and Molly are talking at the start, the amount of bend in Candice's straw changes between angles. (00:05:10)
Continuity mistake: When Molly parks her car right at the start of the film, she parks and then the camera cuts to the two guys talking who walks over to Molly. When he walks over she parks her car again. (00:04:00)
Answer: To answer your first question, Bludworth does in fact mention he has "seen this before", but this means he could have seen these events before the film series ever took place. It is possible that this is where he had learned a lot about death's design. This could even hint at another sequel/prequel. To answer your second question, none of the survivors had been alive to tell the tale of what happened to the survivors of the bridge collapse. In the first few movies, it is noted that the protagonist freaks out, thus, startling MANY people. In the 5th film, Sam is only seen freaking out inside the bus. Even if the FBI have the information, they could have finished the investigation completely, due to Sam, Molly, and Nathan surviving (Until the end of the movie, that is).
M0vi3