Why is the claim that the Isleworth Mona Lisa was painted by Leonardo da Vinci controversial?

The claim that the Isleworth Mona Lisa was painted by Leonardo da Vinci is controversial because it lacks consensus among experts in the field. While some commentators have asserted that the work represents an earlier version of the famous portrait, several leading Leonardo scholars have flatly denied this attribution.1

Unlike the Prado Museum copy, which was confirmed through technical analysis—such as infrared reflectology—to have been created by an assistant in Leonardo’s studio during his lifetime, the Isleworth Mona Lisa does not hold the same scholarly standing. The debate surrounding such works highlights the historical tendency for students and followers to produce replicas of the master's work, often leading to ongoing speculation regarding their origins and the extent of Leonardo's direct involvement.1