> including without limitation the rights to ... sublicense ... the Software.
Sounds like they can distribute that code under the GPL, provided they include the notice (which is OK from the GPL PoV since it doesn't frustrate what the GPL provides). That particular code continues to be available under its original license. The whole is available under the GPL. Licenses are permission to do things that would otherwise be prohibited by copyright; there's no problem with having extra permission or multiple kinds of permission. What part do you think would be a problem?
The license on this file gives extremely broad permission to distribute with no requirements. The GPL has requirements if you are distributing it. These two licenses are not compatible.
Additionally, if they are starting with software under a particular license and modifying it, in a non clean room fashion, then the final product is a derivative of the original and the copyrights likely remain with the original rights holders.
> The license on this file gives extremely broad permission to distribute with no requirements. The GPL has requirements if you are distributing it. These two licenses are not compatible.
That's not how it works at all. You receive the file under a broad license, but can redistribute it under a more restrictive license. Anyone who receives that file under the GPL is subject to the GPL's obligations even if the file previously existed under another license, as long as they weren't actually granted that other license.
This is the entire foundation of "contact me for a less restrictive license"-type monetization schemes. It doesn't matter which licenses the file was ever licensed under, it matters which license was granted to you with the file.
> The GPL has requirements if you are distributing it.
The GPL gives you permission to distribute subject to certain requirements. Having extra permission is not a problem.
> Additionally, if they are starting with software under a particular license and modifying it, in a non clean room fashion, then the final product is a derivative of the original and the copyrights likely remain with the original rights holders.
All of the (nontrivial) contributors to the final project will hold some copyright interest in it. As long as all of them are granting the permission you need, that's not a problem.
Sounds like they can distribute that code under the GPL, provided they include the notice (which is OK from the GPL PoV since it doesn't frustrate what the GPL provides). That particular code continues to be available under its original license. The whole is available under the GPL. Licenses are permission to do things that would otherwise be prohibited by copyright; there's no problem with having extra permission or multiple kinds of permission. What part do you think would be a problem?