I work with copyrights (music).
I and several other former employees of the music publishing company where I used to work "Net4music" operate a business of
writing sheet music from audio supports.
The results are then sent to the SACEM (copyright bureau).
The original creator of a work has a lifelong right to display his work for free, but not to sell it, this is with or without permission of the copyright holder. Therefore as long as no sales are involved the artist has full right to exhibit his work on the internet or otherwise.
A company which holds a copyright cannot renew that copyright after the creator's death.
A personal family member can renew the copyright for up to 50 years after the author's death in the US (100 years in Europe).
Later editions can be copyrighted, but that copyright applies only to the specificities of that edition. The content becomes public domain after 50 years (US).
Anyone can (for example) write thier own arrangement of a song written by a composer who died in 1925. They can copyright that arrangement and even sell it.
But if the author died in 1955 there is a strong possibility that the copyright is still valid.
In the case of the COG. The listed copyright holder no longer exists. It is possible that the rights were sold or transferred to another entity before the dissolution of the COG. In that case there is a danger of copyright infringement.
However if such a transfer were not made then, the material became public domain at the moment the COG was dissolved. No one can now pretend to hold that copyright unless such a transfer occurred before the dissolution of the COG. No new copyrights can be filed after the author's death.