Searching for more books on Napoleon than days since his death on Google shows a few websites that make this claim. Note that Napoleon Bonaparte died roughly 200 years ago, or about 73.000 days ago.
The source most of those websites use is an essay called Review of Books Written about Napoleon Bonaparte which claims
The last estimate for the number of books written on Napoleon was over 300,000 (J.D. Markham, 9)
I don't know what "J.D. Markham, 9" refers to. According to Wikipedia, J. David Markham is an expert on Napoleon Bonaparte. Regardless of who he is though, I'd prefer to see some concrete evidence of this claim to believe it.
Another website says:
Munro Price, quoting yet another biographer of Napoleon, claims there have been “[w]ell over 200,000 books…written about him since his death.”
I wasn't able to find out where Munro Price quoted this "other biographer of Napoleon", let alone who this "other biographer of Napoleon" is.
I've seen mentioned in some places that Amazon references 40.000 books on Napoleon but 1) not all of those books are about Napoleon Bonaparte, and 2) 40.000 is far from 300.000 and fairly far from 73.000 as well.
In the end, I didn't manage to find any primary source, or any explanation of the methodology of those primary sources.
So, have there been more books written about Napoleon Bonaparte than days have passed since his death? Are there more than 300.000 books on Napoleon Bonaparte?