1,000 stardates make up a year on TNG, DS9, and VOY. TNG starts with the 41000s, so the second digit always stood for the season.
In TOS, the stardates are four-digits and progressed unevenly and out of order from the 1000s at the beginning of the series to the 5000s at the end. If you leave out TAS, and pretend all five years were covered over three seasons, then the first digit could stand for the year of the mission; but only if you interpret it that way.
In the TOS movies, stardates seem to move much slower. They're still four digits but the first digit seems to represent the decade while the last three digits don't seem to mean much of anything. So TMP has a stardate in the 7000s, TWOK-TFF have stardates in the 8000s, and TUC has a stardate in the 9000s. Don't try to make too much sense out of it passed that.