[bluGill]

I can't find the details, but this needs to be under the copyright laws of the 1950s, which were very different from today. If they didn't properly register and re-register the copyright over the years the copyright is public domain. A lawyer will need to figure out these details of course.

Edit: of course this case is in Germany, so US law doesn't apply and I claim not information on what their laws are.

[Animats]

European copyright law has broader coverage than US law. Europe recognizes "sweat of the brow" copyright. Some databases are copyrightable in the EU even though there was no human creativity involved. The US does not do that, because the copyright clause in the Constitution limits the reach of intellectual property law. See Feist vs. Rural Telephone (phone directories not copyrightable), Bridgeman vs. Corel (copies of public domain content not copyrightable), and Meshwerks vs. Toyota (3D scans of real world objects not copyrightable). The way new cases are going, AI-created content mostly isn't copyrightable, either.

[bluGill]

How was European copyright law in the 1950s? That is relevant here and I don't know.