Do I have to mention the CC license twice?

Question

In section 3(a) of the Creative Commons Attribution license (and I think all the others too) it says:

1. If You Share the Licensed Material (including in modified form), You must:

   A. retain the following if it is supplied by the Licensor with the Licensed Material:

   • identification of the creator(s) of the Licensed Material and any others designated to receive attribution, in any reasonable manner requested by the Licensor (including by pseudonym if designated);

   • a copyright notice;

   • a notice that refers to this Public License;
   • a notice that refers to the disclaimer of warranties;
   • a URI or hyperlink to the Licensed Material to the extent reasonably practicable;

   B. indicate if You modified the Licensed Material and retain an indication of any previous modifications; and

   C. indicate the Licensed Material is licensed under this Public License, and include the text of, or the URI or hyperlink to, this Public License.

This makes it look like that if the original author notes that the work is licensed under the licensed (which they surely will) you must reproduce that notice, as well as indicate yourself that your publication has used material licensed under the license, i.e. that you must mention the CC BY license twice.

Which doesn't make much sense!

1. How is such a "notice" defined?
2. What is an example of one?
3. How should these two clauses be understood together?

Answer 1

Paragraph A refers to text that was supplied by the upstream author “Licensor”. You're allowed to modify CC BY material, but there are a few things that you need to retain: basically the acknowledgement desired by the upstream author (author identification, copyright notice, license notice, warranty disclaimer, project identification).

Often the upstream author will have included a license notice in the material, and all you need to do to fulfill paragraph C is to retain is as per paragraph A. However, in case there was no license notice, you must add one, otherwise the people you are distributing to would have no way to know that the license applies.

For example, if Stack Exchange was licensed under CC BY-SA 4.0 (it isn't, it's under CC BY-SA 3.0 which has similar but not identical wording in §3.0), then when sharing a Stack Exchange post, you would need to:

• Identify the creator through their Stack Exchange account, respecting the identification attached to the bottom of the post.
• No explicit copyright notice.
• No notice referring to the license inside the work — it's conveyed through the page footer.
• No warranty disclaimer.
• Include a link to the Stack Exchange post.

And in addition you would need to include the text of or a link to the CC BY-SA license, because that didn't come attached to the work.

Another example: if you print out and distribute CC BY-SA material that you obtained on the web, the material may well come with a notice like “Licensed under CC BY 4.0” with a hyperlink to the license. This notice under paragraph A isn't enough satisfy paragraph C, because the hyperlink won't be present in the printed text, the reader would just see “licensed under CC BY 4.0”. Instead you must include the text of the license, or at least print out the URL https://creativecommons.org/licenses/by/4.0/legalcode.