I am not sure we understood each other.
I am not especially asking what NS server is used but suggesting to clarify this on the official documentation.
Forum answers is not reliable in my opinion. They may be errornous and/or updated.
For example, the first visible answer of the topic tells Let’s Encrypt is using Google’s name servers: DNS Servers used by LetsEncrypt for Challenges
This might be confusing for the user, don’t you think?