Let's go through section 3(a) of the license bit by bit.
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;
This is a list of attributive information which can be provided by the original author. They don't all need to be - you could put up a photo online anonymously and say that it's CC BY-SA licensed, and the only one of the list that would apply would be the URL. But, if the author wants, they can. Whichever the author decides to specify, you must reproduce.
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.
I don't really understand why you'd have to reproduce the author's notice referring to the license as well as indicating the license yourself... so I've asked a question about this myself.
- You may satisfy the conditions in Section 3(a)(1) in any reasonable manner based on the medium, means, and context in which You Share the Licensed Material. For example, it may be reasonable to satisfy the conditions by providing a URI or hyperlink to a resource that includes the required information.
So section 3(a)(1)is about what information you must reproduce. Section 3(a)(2) is about how you must do so, and it says that you can do so in any reasonable way.
So my interpretation is that if the original media has an embedded copyright statement saying "© ACME 1999", then you would have to reproduce that, but you don't have to embed it in your modified work in the same way. If you had an attribution section saying the following:
Photo of ACME by ACME, used under the CC BY-SA 4.0 license, http://acme.com
You could modify it to say something like this instead:
Photo of ACME by ACME, © ACME 1999, used under the CC BY-SA 4.0 license, http://acme.com