From the Copyright Alliance, a copyright notice isn't needed to retain full copyright protection, including on new works, since 1989:

https://copyrightalliance.org/education/copyright-law-explai...

"A copyright notice does not need to be affixed to a copyrighted work for the work to be protected under the law.

Prior to 1989 including a copyright notice on a copyrighted work was required under U.S. law, but that is no longer the case. Although copyright notice is no longer required, a copyright owner would be wise to include a copyright notice because it prevents an infringer from raising a defense of innocent infringement."

Furthermore, a copyright year may not be needed if a copyright notice with (c) mark is included.

So the copyright notice is primarily useful as a notice to others with regards to your work, but has no real use as a legal construct to establish ownership.