Enigmatic

Few paintings can have been studied more throughout history than da Vincis Mona Lisa - "the most famous work of art in the world", according to Wikipedia.

Even her expression has come under intense scrutiny - that enigmatic smile - but not to the level those today who appear to be experiencing the Mass Memory Discrepancy Effect. They remember her with a totally blank expression, with absolutely no hint of a smile at all. Looking at her today shows she definitely is smiling, the only argument is to what degree.

Some are explaining this by noticing our brains interpret things differently as we age. Facial recognition is a crucial life skill which develops more as we get older. The thinking is we see a blank expression when we are younger because we haven't "tuned in" enought to recognise her subtle smile. Or, they have been looking at the two different mona lisas (which were painted 11 years apart) without realising it.

In any case, Leonardo wasn't hailed as a genius for nothing.

Is this how she was remembered?

Although clearly exaggerated, this shows the idea behind the Mona Lisa MMDE:

Proof the Mona Lisa has changed over time

There is evidence the painting has changed since Leonardo's day, and a project to digitally restore it to how it would have appeared is described here.