I'm not sure if this is in the spirit of the thread, it's more historical revisionism than it is an anachronism. The WT publications used to teach that Adam, of all people, wrote a portion of Genesis and that Noah's family preserved copies of that portion of Genesis in the ark through the flood.
Also, quite recently, David Splane claimed that the whole of archaeology, historiology and geology are all WRONG because their demonstrated age for the Great Sphinx contradicts the Governing Body's unsupported and egregiously dogmatic interpretation of Genesis.