This is true : We had a 50'ish year old sister in our congregation who had memorized the Kings James Bible. She then could quote both the NWT and KJV versions verbatim. It was quite impressive. (not sure if that included all the "...begat..." in the OT but she could recite the passage in Luke of Jesus' forefathers.
I suspect she was a savant. She was pretty dim about other things.