But it says "In desperation, the Alliance launched 5 sleeper ships." It doesn't reveal the fate of the Hispania in the intro, so why not, if leaving that a mystery, have put 8 sleeper ships and focused on them for the player to eventually encounter in an in game rumour?
The fact is, we have an explicit statement and visual showaround showing a grand total of 5 sleeper ships flying off into space and flying off from wherever it was they had been built. Either aspects of the intro are superseded by developer documents or vice versa.