Am I allowed to add additional copyright on modified code that originally the FSF released under GPLv3

Question

I've ported type_traits from GCC to AVR-GCC with some major modifications to the code structure, style, and used some boost implementations along with some of my own implementations and would like to add my own copyright along with the FSF copyright notice as follows:

Copyright (C) 2020 MyName.
Copyright (C) 2007-2020 Free Software Foundation, Inc.

My intentions are to post it on github as a standalone project.

The problem is I don't know if I'm allowed to because on the one hand you have:

Why does the FSF require that contributors to FSF-copyrighted programs assign copyright to the FSF? If I hold copyright on a GPLed program, should I do this, too? If so, how? (#AssignCopyright)

Our lawyers have told us that to be in the best position to enforce the GPL in court against violators, we should keep the copyright status of the program as simple as possible. We do this by asking each contributor to either assign the copyright on contributions to the FSF, or disclaim copyright on contributions.

We also ask individual contributors to get copyright disclaimers from their employers (if any) so that we can be sure those employers won't claim to own the contributions.

Of course, if all the contributors put their code in the public domain, there is no copyright with which to enforce the GPL. So we encourage people to assign copyright on large code contributions, and only put small changes in the public domain.

If you want to make an effort to enforce the GPL on your program, it is probably a good idea for you to follow a similar policy. Please contact [email protected] if you want more information.

On the other hand:

Am I required to claim a copyright on my modifications to a GPL-covered program? (#RequiredToClaimCopyright)

You are not required to claim a copyright on your changes. In most countries, however, that happens automatically by default, so you need to place your changes explicitly in the public domain if you do not want them to be copyrighted.

Whether you claim a copyright on your changes or not, either way you must release the modified version, as a whole, under the GPL (if you release your modified version at all).

From my understanding they contradict each other, the first prohibits adding my own copyright and the second allows it.

Answer 1

Yes, you may do so, provided you abide by the license of the repository you forked or the code you (re)used. For (L)GPL that means to release the whole code under the same license (or compatible one).

The two statements only seemingly contradict eachother:

The first statement is a requirement the FSF has when you like to contribute directly to one of their projects. That is, if you want to create patches or contributions which shall be merged into the project itself. They do want a written consent to transfer copyright or the rights to the changes as far as allowed by laws to allow a future change of license without the need to aquire consent by every party who previously contributed to the project. This is a method frequently applied to allow a project to remain functional while having many contributors which might make single contributions and leave afterwards. This question and paragraph about copyright assignment to the FSF does not apply for forks or code re-use outside of repositories of their ownership - like your repository. There you only have to abide by the license terms (of the GPL, LGPL or whatever is used at the time of forking).

The second statement is a general statement on how copyright law works - if no other statements or contracts are made to change the defaults.