" The answer was because you were in a different sector of the universe.'  The following instructions to writers were copied from the series bible Star Trek Guide; they are quoted at Star Trek Fact Check.
 The original date of composition and the author are unclear, but the sample stardates are consistent with the range from the second pilot.
( In an alternate timeline that diverged from the prime timeline in 2344, the term combat date had replaced the term stardate in the dating system used by Starfleet by 2366.
I felt that that sounded a little awkward for the 23rd, 22nd century, so I thought that there should be another, another dating system.
We invented "Stardate" to avoid continually mentioning Star Trek's century (actually, about two hundred years from now), and getting into arguments about whether this or that would have developed by then.
Pick any combination of four numbers plus a percentage point, use it as your story's stardate.
An overall increase with time can be observed in the above table of stardates, from 1312.4 in the second pilot to 5928.5 in the final episode of the series.
The Animated Series and the movies continued the general trend, despite a number of variations in the rate of change.
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'So the stardate on Earth would be one thing, but the stardate on Alpha Centauri would be different,' Peeples says.