Einstein, in his special relativity, DID fully address simultaneity-at-a-distance according to a perpetually-inertial person (the "PIP"). According to the PIP (she), a distant person who may be accelerating in any way he chooses (the AP), is at each instant ageing slower than the PIP by the well-known gamma factor (which is a function only of the his speed v relative to her, according to her, at that instant). So by integrating those relative ageing rates, the PIP can determine the current age of the AP at each instant of her life. She can thus produce a plot of his age (on the vertical axis), versus her age (on the horizontal axis) ... I call that "the age correspondence diagram" (the ACD), according to her (the PIP). But as far as I know, Einstein never addressed the question of simultaneity-at-a-distance, according to the person who sometimes accelerates (the AP). How does the AP produce the ACD that gives the distant person's (the PIP's) age at each instant in the life of the AP? And why did Einstein never address the question?