the call letters of a vessel which has been missing for over two centuries ... another Earth ship
From that we don't get how long it was between the time the Valiant left Earth, until the time it "disappeared." Couldn't have been too many years, but still maybe not immediately after departure.
Nor do we get any sense of how long it was between the time of the Valiant's disappearence, and when the Valiant arrived at the energy barrier.
Could have been decades.