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.
Speculations about Mona Lisa
In 2005 Heidelberg University academics discovered notes scribbled into the margins of a book by its owner in October 1503. These notes state that Leonardo is working "on the head of Lisa del Giocondo". This is seen by some as confirmation that a certain Lisa del Giocondo has been the sitter for the "Mona Lisa". However, these notes offer no description of the painting or drawing and could be attributed to any female portrait of that time.