The definition includes «في عصر»—in one period. It concerns jurists of a particular era agreeing about a matter, not a selective collection of opinions from different centuries.
If all qualified jurists of a period are shown to agree on a ruling, the definition can apply. Yet finding several prominent scholars who adopted the same opinion across centuries does not by itself establish consensus.
This lesson deals with the conceptual grades of ijma‘. Establishing that a particular historical consensus actually occurred is a separate evidentiary task.