So Creative Commons does not call CC0 a license, but rather a tool. The six CC licenses are BY, BY-SA, BY-NC, BY-NC-SA, BY-ND, and BY-ND-NC, all of which have the attribution (BY) clause, while CC0 has a statement by the author dedicating their work to the public domain (which is not a license, since a license is an agreement between the rightsholder and a user of some copyrighted work – rather, it is a public declaration of their action of dedication of the work to the public domain) … which works in countries where that is permitted.
Oddly, there are some countries (not many), where rightsholders are not permitted to put their works into the public domain, and in these jurisdictions there is a fallback license in CC0 which allows any potential user to do whatever they want to with the work, exactly as if it were in the public domain.
(Actually, there is then a third and final layer to CC0 where the rightsholder promises not to exercise any control over the work whatsoever (exactly as if the work were in the public domain), in jurisdictions where there is some technical reason for which the first two layers are not working.)
CC has another tool related to public domain: the public domain mark, which users can put on a work when they are showing the work, if they know the work to be in the global public domain. For example, museums use this when showing very old works.
As for the thing you noticed, Alan, about both names given… I’m not 100% what is intended by the way they have described rights. What I see on the page CommonLit | Someone Might Be Watching — An Introduction to Dystopian Fiction | Free Reading Passages and Literacy Resources is
“Someone Might Be Watching — An Introduction to Dystopian Fiction” by Shelby Ostergaard. Copyright © 2017 by CommonLit, Inc. This text is licensed under CC BY-NC-SA 2.0.
Unless otherwise noted, this content is licensed under theCC BY-NC-SA 4.0 license
right under the text, and then
© 2014-2021 CommonLit. ™
at the bottom of the page.
The one at the bottom just seems to be about random things on the page, and the page itself. As for the work shown on that page, it seems that the author is this person Shelby Ostergaard but the rights are held by CommonLit. This is only really important in reusing this work, either by copying or adapting it, whereupon you have to give a careful attribution to the work. Now rightsholders can say if they want attributions to their works done in a certain way, so what I would probably do with this work is, when making a copy of this work, to give an attribution like
“Someone Might Be Watching — An Introduction to Dystopian Fiction” by Shelby Ostergaard is licensed under CC BY-NC-SA 2.0 by CommonLit.
where the part “Someone Might Be Watching — An Introduction to Dystopian Fiction” would be a link to the URL www.commonlit.org/en/texts/someone-might-be-watching-an-introduction-to-dystopian-fiction, the CC BY-NC-SA 2.0 would be a link to the URL creativecommons.org/licenses/by-nc-sa/2.0/ and the CommonLit would be a link to the URL www.commonlit.org … because it would be my interpretation that that is what they want by giving that licensing/copyright statement. … But, of course, IAmNotALawyer!
One last point: I don’t know that I agree with a point made earlier in this thread that the 2.0 version of the license only applies to the work in the past, while the 4.0 version applies now. It is true that more recent versions of a license are considered compatible with older versions, so that, for example, if you adapted this work, you would have to put a CC BY-NC-SA license on your new adaptations (because of the SA), but you would be free to put any version of BY-NC-SA from 2.0 to 4.0 on it, since they’re all compatible with the old 2.0. CC strongly recommends that you always use the most recent version of the license suite whenever you newly license something, so that advice would imply you should license your new adaptation as BY-NC-SA 4.0.
However, that license on the new adaptation doesn’t change the license on the original work, which keeps its old license. This issue actually has some teeth! For example: one of the big issues with the 4.0 version of the license suite is that a user who is not correctly complying with all of the parts of the license has 30 days to fix those errors after being notified of them, and then will be considered in compliance. Earlier versions did not have this. So it turns out that there are some copyright trolls in Germany who are posting media on sharing sites with older versions of the licenses, and then if anyone uses one of those files with even the tiniest mistake in their attribution, the license is instantly and irrevocably violated, whereupon the troll can go after the user as having made a copyright violation with potentially a large penalty. Some users have been caught with this and have had to pay large sums to the trolls. All of which, of course, only applies because that old license version sticks to the work and the user today cannot say “I prefer to be subject to the terms of the 4.0 version of the license, not the 2.0 (or 3.0) version which the work says it is released under.” See what I mean?
BTW, sorry I went on so long … but I’m kind of obsessed about all of this stuff. It’s fairly intricate, but if anyone is interested, I strongly recommend taking the Creative Commons Certificate course (see https://certificates.creativecomms.org) which leaves one a complete expert on all of it!