If they did this how long before Windows XP Mint was released?
More seriously, how much of their code could they release without giving away much of their next operating system. Certainly by the fact that this bug effects versions of the OS going back 15 years we can be relatively certain that the code contained between them has a lot of identical parts.
"Release the source code" does not necessarily equal "allowing people to make derivative products from it". You could release it under a strict "only to be used to fix defects"-license.
It wouldn't be "open source" or "free software" as we understand it today, but I don't mind, and it's a lot better than what we have now.
More seriously, how much of their code could they release without giving away much of their next operating system. Certainly by the fact that this bug effects versions of the OS going back 15 years we can be relatively certain that the code contained between them has a lot of identical parts.