Yes, interesting shift in perspective that hackers now kind of use blackhat-techniques to do forensic analysis in regards to ownership. In the earlier days we cracked games to hypocritical free them of their perceived handcuffs. Hence "Free Software". Code was free and can be used and reused by anybody.

Of course due to litigation and legal implications the statements in Masters of Doom are intentionally vague. The same goes for the founder's talks. No one lied or portrayed themselves in a ubermensch fashion, it was just talking in corporate language speak when you are not allowed to provide more details in public. There seems to be serious legal risk and maybe it got solved or not, but judging from the book's perspective, I believe that they solved the issue in combination with a non-disclosure agreement.

I think that the "Great artists steal" mantra is especially applicable to ID's early days. And code reuse is simply a variance - stealing from yourself.

In no way does the usage of third party libraries damage the ID myths. For example, owning IP and authorship is not the same. Also: one can use a programming framework for a below average app while another one builds an awesome app.

And this is what's MoD underlying theme: going your own way because you see a chance while staying in the current context. In the end, ID did what Softdisk did: developing and publishing games. One only with moderate success while the other conquered the world.

Latin alphabet epitomizes this day by day. 26 letters which seem laughable, but a fool with a great tool is still a fool. ;)