condition allows for the physical possibility and likelihood that they will not be simultaneous from the standpoint of another reference frame.

But outside special relativity, the coordinate time is not a time that could be measured by a clock located at the place that nominally defines the reference frame, e.g. a clock located at the solar system barycenter would not measure the coordinate time of the barycentric reference frame, and a clock located at the geocenter would not measure the coordinate time of a geocentric reference frame.