Also, the Enterprise was capable of traveling much faster than Warp 10, well before it was established that this was the unattainable speed that would you to "occupy every point in space at the same time."
That wasn't settled on until TNG, and not until after the early first season (since Geordi said in "Where No One Has Gone Before" that they were passing warp 10). Roddenberry arbitrarily decided that warp 10 should be an absolute cosmic speed limit, and then the tech people decided to equate it with infinite speed -- which, if you think about it, is the exact opposite of a speed limit. Which has confused a generation or more of fans, since using a finite number to represent infinity is sending mixed messages.
(The reason you'd occupy every point at the same time at infinite speed is because any number divided by infinity is zero -- or rather, the limit of n/x as x approaches infinity is zero -- so the infinite-speed travel time between any two points regardless of distance would be zero. Basically it's just an unnecessarily complicated way of saying "infinite speed," another way that the explanations of warp 10 just confused the issue.)