ok, maybe you are right and thats the reason why unsplash changed it from "CC0" to "unsplash license".

if I read the official CC0 Page it fits completely https://creativecommons.org/publicdomain/zero/1.0/deed.en

I will study the topic even more and provide a suitable declaration. https://creativecommons.org/publicdomain/zero/1.0/legalcode

thank you