Why one Roman legion could appear in several places

Could more than one Roman legion with the same number serve at the same time?

Usually not as complete legions, but detached vexillations from one legion could operate in several places at once.

Roman armies did not normally maintain several complete legions with the same number at once. Confusion arises because a vexillation could be detached from its parent legion and sent elsewhere. One portion of the Twentieth might therefore remain at its base while another fought in a separate theatre. The distinction matters when inscriptions or campaign accounts seem to place the same legion in two locations simultaneously.