https://www.youtube.com/watch?v=ovD0aLdRUs0
The Saturn V F-1 rocket engines were hand made! The engineers almost solved problems on the spot, and so the engineers were living relics of how to build those engines. When they died, their secrets died with them.
One should further note that the size of the project, in terms of the amount of people working on everything from the F-1 engines to each and every stage of the Saturn V. Nobody knew everything about what everyone else did.
Getting to the SpaceX BFR(Big Falcon Rocket), i'm hearing engineers say that their Raptor engine and the BFR that they've seen so far is a unique design with unique solutions to problems.
I saw this one comment, somewhere, from SpaceX second or third in command . . . i forget her name right now . . . she said "yea, well, we built that Raptor engine." That's in responce to someone wondering how they solved some problem with not that much money(Elon Musk isn't quite as rich as say, Nasa for one, and Jeff Bezos of Amazon for the other; his SpaceX team has been at it for a longer time).
