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.
Lisa del Giocondo
During the spring of 1503, Leonardo had no income source, which may in part explain his interest in a private portrait. But later that year, he most likely had to delay his work on "Mona Lisa" when he received payment for starting "The Battle of Anghiari", which was a more valuable commission and one he was contracted to complete by February 1505. In 1506 Leonardo considered the portrait unfinished. He was not paid for the work and did not deliver it to his client. The artist's paintings traveled with him throughout his life, and he may have completed the "Mona Lisa" many years later in France, in one estimation by 1516.