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.
Salvator Mundi (Leonardo)
Referred to as the "Last da Vinci", "Salvator Mundi" was the only known painting by Leonardo still in private hands. Fewer than twenty other known works by Leonardo are held in museums around the world, including the "Mona Lisa" and "The Last Supper". The only work by Leonardo in North America, "Ginevra de' Benci", is held at the National Gallery of Art in Washington, D.C. The museum purchased "Ginevra" in 1967 for $5 million in a private sale (equivalent to approximately $36.4 million in 2017), a world record at the time. "Salvator Mundi" is the first painting by the artist to appear in a public sale for 100 years.