CC0 is explicitly designed with such legal issues in mind and includes a license for legislations that do not have direct way of putting works to PD

> If the waiver isn’t effective for any reason, then CC0 acts as a license from the affirmer granting the public an unconditional, irrevocable, non exclusive, royalty free license to use the work for any purpose.

https://wiki.creativecommons.org/wiki/CC0_FAQ#How_does_it_wo...

https://creativecommons.org/share-your-work/public-domain/cc...