Thanks Timo. So basically the dialogue from Starfleet crewmembers for Warp 9.975 is before Voayager was knocked into the Delta quadrant and started taking damage. I mixed up the "Relativity" episode
From "Barge of the Dead":
NEELIX: Fifteen decks. Computers augmented with bio-neural circuitry. Top cruising speed, warp nine point nine seven five, not that you'll be going anywhere.