The Gemara doesn’t use the word Golem. It started at some point. True, he doesn’t say it was the Maharal. But I am showing that the story was around. And, as others have said in the past, not necessarily was it a well known fact. Those that bumped into it knew about it.
The question is, how would the Meshumad know how it was made?
You shouldn’t comparee what you found in a book to a book itself. You are saying that not everything printed is true, and I am am saying that a book with an author was authored by that author. I didn’t see anyone questioning its authorship. All online articles seemed to be aware of the Shlangenbald.
Old books are constantly used as ‘documented proof’. I never noticed the requests to see the original manuscripts. Do you ask, how do we know the Maharal wrote Be’er Hagolah and Derech Chaim? Did you see the manuscripts?