Multiple realities
(covers information from several alternate timelines)

ECS was a registry number prefix for both Earth and Federation starships.

In the 22nd century, the Y-class freighter ECS Fortunate bore the registry number ECS-2801. (ENT: "Fortunate Son")

In the 2250s, in the alternate reality, the USS Kobayashi Maru, the titular ship in the Kobayashi Maru scenario, bore the registry number ECS-1022. (Star Trek)