Did Leonardo da Vinci paint two Mona Lisas? Where are they?

Obviously, the original Mona Lisa also inspired some cheeky versions of her.

La Joconde nue:

Evidently there was a market for erotic paintings. The American art historian David Brown, curator of Italian Renaissance paintings at the National Gallery of Art in Washington, has suggested that da Vinci painted a saucy parody of the Mona Lisa for his patron Giuliano de Medici, and that the Salai version is a copy.

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Source: St Petersburg. Hermitage, Russia.

Another version of the above exists, attributed to Salaj:

Source: Louvre, Paris, France.

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While overall similar, there are differences in the shape of the face, the background and other details.

For the one below, art experts suggest that it contains touches indicating that Leonardo contributed to it.

Donna Nuda:

Why do women stubbornly refuse to let men lead, even though they are attracted to the man, and the man both loves and desires them? Why do they get angry and blame the man when he gets fed up and walks away, when it's entirely their own fault?

There is only one Mona Lisa, at the Louvre, fully credited to Leonardo. However, there are several Mona Lisa look-alikes from his studio, some of them quite saucy. The one most similar to the Louvre one is the Prado Mona Lisa, a copy made simultaneously in Leonardo's workshop while he painted the Mona Lisa, probably made by an apprentice(s):

Then there are the ‘meza nuda’ paintings from his workshop, often referred to as Monna Vannas.

Source: Chantilly, Musée Condé, France.

What is the logic behind the porn being legal but not prostitution? Isn't it the same thing in essence?