I think what fascinates me the most about all of this is how there are wide gaps in how much design and engineering documentation from that time period has survived to present day. For a long time, I just assumed that NASA owned and archived every design spec, revision, research paper, memo and napkin doodle related to their public-facing missions. I learned recently that even a lot of the original Gemini and Apollo program code (let alone source code) and docs are apparently gone forever.