I would assume they would have a couple of such devices running since publication till now. Instead of >24 hours they probably know the endurance after about 50

I would assume they would have a couple of such devices running since publication till now. Instead of >24 hours they probably know the endurance after about 500 days today, allowing for more convincing extrapolations towards 10^7 hours. It is unclear from the article if these plots are tests of individual memory cells or a large collection of cells. Any serious attempts would involve an array of cells so a million such graphs can be plotted together etc.