Earlier quoted context omitted.
> You can't retroactively un-GPL any copies that other people already have That's what I meant when I said that you can't revoke the GPL. Of course with new versions you have more freedom, but what was relased under the GPL remains available under the GPL.
> but what was relased under the GPL remains available under the GPL. Not necessarily. The copyright holder only has to provide source to those who got it from them under a GPL license. Others may not be able to get a copy, as those who can ask you for it aren’t obliged to give it to them on request ( https://www.gnu.org/licenses/gpl-faq.html#CanIDemandACopy ) There also is the issue as to what happens when a license…
perhaps, in line with what you are saying, t would be better to express this as;
"but what was obtained under the GPL remains obtained under the GPL."
In other words, at a moment in time, a user can request the source of the (GPL) product they are using. They have rights and obligations for that code as it exists then.
It does not give them a right to any later versions of that code. And it does not allow the author to retroactively "deny" the rights they have.
One of the rights they have is to publish that code. (more accurately they can publish something based on the code, and hence by extension pass on the code to more users.)
Nothing says the original author as to keep the GPL version in any kind of public place. And the original author (assuming he has 100% copyright) can of course build on that code himself, and release the new code (or indeed the same code) under a different license.