Licensing when Porting

Question

So I recently found some homebrew software for the Nintendo DS (NDS) which I like to use. But I have a Nintento 3DS (3DS) with homebrew enabled and I am thinking about porting it to the 3DS. I want to make it open source and on github.

Now the source code only has a license.txt (GPLv2) in the root directory. There's no sign of a copyright line in any of the source files or readmes. Does the license.txt in the root by itself actually enforce the license on to the code?

There are however names in the credits section in the readme.txt, does that entitle copyright to the people mentioned?

To actually use the GPLv2 it states to include some kind of line in the source?

Like so:

one line to give the program's name and an idea of what it does.
Copyright (C) yyyy  name of author

Since there is no such line anywhere, is this source code actually using GPLv2?

The ultimate answer I'm after is: can I use a different license (GPLv3, MIT) when porting it to a different platform or should I stick with GPLv2?

It's more like I'm starting a new codebase but following the design and maybe some of the code from the old one.

Answer 1

You seem to be confusing copyright with licensing; they are not at all the same thing.

Does the license.txt in the root by itself actually enforce the license on to the code?

Yes.

There are however names in the credits section in the readme.txt, does that entitle copyright to the people mentioned?

It doesn't matter. You don't have, nor do you need, copyright; you only need a license.

To actually use the GPLv2 it states to include some kind of line in the source?

Like so:

one line to give the program's name and an idea of what it does.
Copyright (C) yyyy  name of author

Since there is no such line anywhere, is this source code actually using GPLv2?

Yes. Copyright does not have to be asserted to be valid, though it's always a good idea to do so.

Can I use a different license (GPLv3, MIT) when porting it to a different platform or should I stick with GPLv2?

You should stick with GPLv2.

You can't change it to MIT because GPLv2 does not allow you to remove the "freedoms" it provides (specifically, the copyleft provision).

You can't change it to GPLv3 because the GPLv2 license states that code covered by it can only be distributed under the same license.