Isleworth Mona Lisa
According to Leonardo's early biographer Giorgio Vasari, Leonardo had started to paint "Mona Lisa" in 1503, but "left it unfinished". However, a fully finished painting of a "certain Florentine lady" surfaced again in 1517, shortly before Leonardo's death and in his private possession. The latter painting almost certainly is the one that now hangs in the Louvre. Based on this contradiction, supporters of the authenticity of the "Isleworth Mona Lisa" claim it is the unfinished "Mona Lisa", made at least partially by Leonardo, and the Louvre "Mona Lisa" a later version of it, made by Leonardo for his own use.
Seymour Reit
Reit wrote over 80 books, primarily for children, on a variety of historical, technical, natural, and other subjects. One of his titles for adults, "The Day They Stole the Mona Lisa", written in 1981, is about the theft of the Mona Lisa from the Louvre in 1911. In the book, Reit asserted that there were "two" genuine "Mona Lisas" in the world: the one in the Louvre, and an earlier version of the work painted by Leonardo da Vinci which was being held in a bank vault in New Jersey (the so-called "Vernon Mona Lisa"). A long-planned movie adaptation of the book has never materialized, although the Internet Movie Database lists a movie by the same title tentatively planned for 2009.