These secondary objects are called hrönir and are, though awkward in form, slightly longer. Until recently, the hrönir were the accidental products of distraction and forgetfulness

Frank and open was the exchange of views at the ECVP-2014 meeting in Belgrade a few months back when Claus-Christian Carbon presented his analysis of the Emergency Back-Up Mona Lisa recently uncovered (literally!) in the Prado, much in the manner of a hrön.*

I do not know if the Ignobel Prizes include a special award for "Scientific Innovations Illustrated with Lego Figures", but if there is, Carbon and Hesslinger's work is a serious contender. They propose that the Prado version is not a copy, but was painted in parallel with Leonardo's original, by a trusted apprentice peering over the Master's shoulder -- the slight parallax explaining the discrepancies between the two.**

These discrepancies also discredit the accepted account for Cloned Giocondas. That's the one with a time-unstuck alien coercing Leonardo into knocking off multiple copies so that his 1970s avatar can exploit them in a heist plot to make enough money for time-travel research... the City of Death theory for short.

However, the possibility remains open that the differences between versions represent not coigns of vantage, but different instants of time, painted by Leonardo for an early peepshow animation. The future discovery of the remaining frames -- between them recording the full cycle of activity -- is practically guaranteed by the workings of the morphogenic field (intensified as it is by each previous version).

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* "The methodical fabrication of hrönir has performed prodigious services for archeologists. It has made possible the interrogation and even the modification of the past, which is now no less plastic and docile than the future."

At Riddled we do not rate for the hrönirific approach to recovering Mona-Lisa variants for it requires the elimination of "witnesses who knew of the experimental nature of the search". We have suffered enough problems with staff retention after the confusion between 'Gioconda' and 'anaconda' while procuring materials, such as could happen to anyone, and entirely due to someone else's bad handwriting.

** The apprentice is thought to be either Giacomo Salai or Francesco Melzi but confirmation awaits further research into conversations in the studio. These can be reconstructed (as any fule kno) from the slight sinusoidal oscillations in the paths of individual paintbrush hairs vibrating in the ambient sound, and then captured in the drying paintstrokes.

Bonus Reverse-correlation perceptual study of La Gioconda here.

Useful lynx at Griffonage-dot-com; also bonus animations.