The main theory is that Leonardo Da Vince and his students painted the same person, piece, or woman around the same time and in the same style and this may have been the equivalent of a modern art class.

As an example of similarities, you could check out the Isleworth Mona Lisa which is thought to predate the more well known Mona Lisa. Also of note is that it is unknown if Leonardo painted any of these or all of them (and may have started or touched up several of them and let his students finish them... we just don't know)... and that includes the original, but most of them likely came from his studio and can be dated to the period he could have done them.

Edit:// here is another Mona lisa, (a twin to the original, also is displayed in OP's linked article) painted and even has the same errors/changes made to the original but is believed to have been painted by one of his students. As you can see the color choice and overall look is different despite it being the same person painted.