>The missing proprietary bits were not their own code. There was nothing to read and no documentation. They could see the call, and that something important happened, but what it did and how it should work was guesswork.
To your point, the following link is another famous example of smart programmers not being able to easily understand someone else's source code. Raymond Chen at Microsoft couldn't easily figure out why Pinball didn't work in 64bit Windows and gave up:
https://devblogs.microsoft.com/oldnewthing/20121218-00/?p=58...