I'm sure it is true. See Bridgeman Art Library v. Corel Corp . Yes, there is a real-world effect. As I mentioned and jeffmould wrote, I can use those part of P

I'm sure it is true. See Bridgeman Art Library v. Corel Corp . Yes, there is a real-world effect. As I mentioned and jeffmould wrote, I can use those part of ProjectB which came from ProjectA without being subject to the teamhappy license of ProjectB. It's not a question of dual licenses, it's one of license compatibility. If I am IBM, and SCO sues me because my distribution of the Linux kernel contains code which is part of Unix, whose copyright is controlled by SCO, and without an SCO license, then a valid response is to point out to SCO (and the court) that that shared code was released into the public domain by AT&T. Even if some Linux kernel developer actually did copy the code from SCO Unix (very unlikely!), there is no new copyright claim by SCO for "slavish" copying.