I was going to comment about fogbank as well, this article explains the efforts the Govt. tried to reverse engineer the substance - https://www.washingtonexaminer.com/weekly-standard/the-fog-o...

Also it is no longer known how to make the Saturn V rocket which flew to the moon - https://www.nytimes.com/1987/05/26/science/hunt-is-on-for-sc...