Before revision:  An interesting phenomenon that the growing trend of  lifespan differential at the beginning of the studied interval does not persist, i.e. that it reverts to stagnation or even decline is revealed for a large majority of countries in the dataset.
After revision:  An interesting phenomenon that the growing trend of the observed lifespan differential at the beginning of the studied interval does not persist, i.e. that it reverts to stagnation or even decline is revealed for a large majority of countries in the dataset.