Hi Pine,
TL;DR: best to just say it's the largest encyclopedia ever. That should be safe.
Claims like this are hard to make because terms that seem concrete from afar tend to break down up close. For example: What do you mean by largest?
Largest in bytes? Words? Content "units" (articles vs. manuscripts in this case, I guess)? Contributors?
What do you mean by "open text project"? Is
archive.org an open text project? It has 8.2 million books. How would you compare the two? Does 1 book = 1 article?
Having said all that, I'm curious how others have/would craft a claim like this. My guess is that most of us who've written for an academic audience have settled for some variant of "largest encyclopedia" (you've got to put something in your Introduction paragraph, after all). What sayst?
J