Version control practices have changed a lot since the 70s. It's possible the code has actually been lost. Or, more likely, the version that actually runs has b

Version control practices have changed a lot since the 70s. It's possible the code has actually been lost. Or, more likely, the version that actually runs has been lost. Some code still exists (or existed), but how exactly it differs isn't exactly known, and deploying it would require getting a higher up to sign off on, essentially, unbounded risk for their critical systems (they will never do this). If that happened in the 80s or 90s the code that exists has probably diverged enough that it's effectively pseudocode at this point.