I believe that Horne revealing the 2 separate "Briefing Board" sessions was ground breaking. That + Horne unearthing Dino Brugioni = an evolving Zapruder Film. What we have today is Not what Dan Rather viewed and described to the nation.
Doug Horne's description of the missing autopsy photos during the hearing is especially informative and important. He starts talking about the missing autopsy photos at 56:45: https://www.youtube.com/watch?v=QPOFi_6Bk-4.Dan Hardway's testimony about his and Lopez's finding that Oswald was impersonated in Mexico City is also informative and important. Same link.