This claim seems to be going back all the way to the 1990's. As an example, in her ARRB testimony Ann Goodpasture said "there are 2,000 – over 2,000 books already been written."
I heard James Tague once say he owned 500 books in relation to the Kennedy assassination and Walt Brown say he amassed a library of 1000 books in relation to the assassination. I don't know how many books are in the 6th Floor Museum library. One would presume that library would have pretty much every book ever written on the assassination.
Is the 2000 books claim true? And how many books are there now in 2021 I wonder?